Can't find where to connect rear center seat belt

Heating and the cooling both don't work ? Just one seat or all seats ?
Your best bet have it checked for DTC'S - diagnostic trouble codes to start .
Climate Controlled Seat Module (CCSM) Diagnostic Trouble Code (DTC) Index DTC Description Source Action B1342 ECU Is Faulted CCSM INSTALL a new CCSM and CARRY OUT programmable module installation (PMI). REFER to Climate Controlled Seat Module . B1358 Ignition Switch or Blower Electronics Circuit Short to Ground CCSM Go To Pinpoint Test Q . B2477 Module Configuration Error CCSM This DTC indicates programmable module installation (PMI) has not been done to a newly installed module. CARRY OUT PMI. REFER to Section 418-01 . CLEAR the DTC. CARRY OUT the self-test. B2486 Climate Controlled Seat Module Voltage Out of Range CCSM DEPOWER the supplemental restraint system (SRS). REFER to Section 501-20B . DISCONNECT driver safety belt buckle pretensioner electrical connector or passenger safety belt buckle pretensioner electrical connector of the affected seat and CONNECT restraint system diagnostic tool 418-F395 to the safety belt buckle pretensioner harness connector. CONNECT the battery ground cable. CHECK circuit 294 (WH/LB) for a fault. REPAIR as needed. If okay, REFER to Section 414-01 . Once the repair is complete, DISCONNECT the restraint system diagnostic tool from the safety belt buckle pretensioner harness connector and CONNECT the safety belt buckle pretensioner connector of the affected seat. REPOWER the SRS. REFER to Section 501-20B . B2488 Thumbwheel Switch Voltage Out of Range High CCSM Go To Pinpoint Test R . B2521 Tach Circuit Failure CCSM Go To Pinpoint Test Q . B2729 Cushion Over-Temp Detected CCSM Go To Pinpoint Test S . B2730 Back Over-Temp Detected CCSM Go To Pinpoint Test S . B2731 Differential Temperature Fault CCSM Go To Pinpoint Test S . B2792 Heat Switch Short to Ground CCSM NOTE: If HEAT is pressed for greater than 20 seconds on the climate controlled seat switch, DTC B2792 will set in the CCSM.
CLEAR the DTC. If the DTC does not clear, DEPOWER the supplemental restraint system (SRS). REFER to Section 501-20B . DISCONNECT driver safety belt buckle pretensioner electrical connector or passenger safety belt buckle pretensioner electrical connector of the affected seat and CONNECT restraint system diagnostic tool 418-F395 to the safety belt buckle pretensioner harness connector. CONNECT the battery ground cable. CHECK circuit 1551 (VT/WH) for a short to ground. REPAIR as needed. If okay, INSTALL a new climate controlled seat switch. Once the repair is complete, DISCONNECT the restraint system diagnostic tool from the safety belt buckle pretensioner harness connector and CONNECT the safety belt buckle pretensioner connector of the affected seat. REPOWER the SRS. REFER to Section 501-20B . B2793 Cool Switch Short to Ground CCSM NOTE: If COOL is pressed for greater than 20 seconds on the climate controlled seat switch, DTC B2793 will set in the CCSM.
CLEAR the DTC. If the DTC does not clear, DEPOWER the supplemental restraint system (SRS). REFER to Section 501-20B . DISCONNECT driver safety belt buckle pretensioner electrical connector or passenger safety belt buckle pretensioner electrical connector of the affected seat and CONNECT restraint system diagnostic tool 418-F395 to the safety belt buckle pretensioner harness connector. CONNECT the battery ground cable. CHECK circuit 1550 (WH/OG) for a short to ground. REPAIR as needed. If okay, INSTALL a new climate controlled seat switch. Once the repair is complete, DISCONNECT the restraint system diagnostic tool from the safety belt buckle pretensioner harness connector and CONNECT the safety belt buckle pretensioner connector of the affected seat. REPOWER the SRS. REFER to Section 501-20B . U2362 UBP Invalid Data Node ID CCSM NOTE: DTC U2362 indicates a network concern, the CCSM is not the source of the fault.
CLEAR the DTC. If the DTC does not clear, REFER Section 418-01 .

I would say the sensor in the buckle has failed.

If I had the problem I would look at a junkyard or on line at e-bay for a replacement. You will need to get the buckle and the belt that it is attached to that goes down to the floor down through the crack in the seat.
Remember the buckle receiver is made for the certain belt in the front and rear seats. I have often tried to put the wrong belt in a buckle and it would not fit. ( Example: the right belt goes in the right buckle.)
Be blessed.

On my 2016 Ford Escape the rear passenger seat folded down and would not hold back up the problem was that the seat belt buckle pivoted down below the level of the seat when I try to raise the back of the sheet the seat belt buckle would prevent it it ended up crushing the plastic on the seat belt buckle preventing it from working the hold the seat belt I was able to repair the seat belt buckle with a screwdriver regular Style and a cigarette lighter the soft in the plastic back up so it would stay in position

check to see if the wire has came loose leading to the seat belt disconnect button you push when releasing the seat belt if connected. then will have to replace that part of your seat belt the sensor or switch in buckle may have broke

i think my new 2012 toyota corolla back seat seat belt are put in incorrectly from factory.

the right belt clip buckle clip says"Center" when it should be right, and the center is the right. so when i buckle the back seat belts they are kinds crossing each other . Why ? any suggesions?

The rear seatbelt of the forester was a bit of a puzzle for me as well when we first got ours. The buckle is really in two parts. The first part anchors the strap, and the second part secures the occupant.

Check if your belt is fully retracted, look in the inertia reel housing at the roof in the boot of the vehicle. Remove it passing the end through the 'loop' in the backrest Make sure that you have the two buckle parts I referred to earlier. There should be an odd looking buckle fixed at the end of the belt, and the more familiar buckle that slides up and down the belt. The end buckle goes into the receptacle vertically below the loop between the centre and window passenger and achors the belt in place. This buckle should not be normally released once used regularly. Once the centre passenger is in place, use the sliding buckle as you would for any other seatbelt and fasten on the receptacle on the other side to secure.

Use same procedure for fixing a car seat or booster, etc.

The rear seat pulls out easily.  Grab the front of the seat with fingers under seat on driver side and pull up hard.  do the same on the passenger side and it will unclip.  Then you can move the seat around to get to the buckle.  Install by inserting rear end in first and lineing up the metal tabs w/ the female plastic inserts in the floor and push down hard until it snaps into place.

I need to replace the rear passenger-side seat belt buckle clasp but the clasp (under back seat) is connected to the seatbelt for middle backseat passenger.Can I replace just the passenger side without disturbing the middle belt?, cheers,Jen.

Soak it soak it and soak it....... may take a few days.... If nothing works, get a hair dryer and heat it up warm to the touch..... melt wax all over the quite warm bolt unit and let sit overnight.... as it cools it will draw the wax down along the threads