I have a santa fe 2005 with 2 rows of seats. I fold down the single back right seat I can no longer access the seat belt buckle for the center seat because it is located under the now folded down seat

SOURCE: Rear seat won't fold down (60 part of 60/40 seat)

I had the same problem on my '03. The seats would not fold down using the latch release as I had always done. So I tried a combination of pulling up on the side latch AND the top latch and the seat folded down. It really doesn't FIX the problem but circumvents offending  defective part. I will use this method until it doesn't work then I might shell out the $$$$$ to the dealer.

SOURCE: how to fold down back seat

There should be a loop between the seat and backrest, pull that and the seat will pull toward the front seats. After that, pull the lever located at the outside of the backrest. This lever is on the outside of the seat by the door-side of the seat. Pull that up and allow the backrest will fold down and the headrest will pivot back and your seat is folded down.

SOURCE: rear folding seat belt locked

get your dealer to replace the seat belt, depending on age, should be under warranty. Belt is defective. I have a g 2003 vue, and my dealer replaced the belt for no charge.

SOURCE: middle row back seats...how can

first fold them flat then pull the handle which will release the rear bottom brackets and allow you to pull back and lift the entire seat out of the van....both seats.

SOURCE: 2003 Toyota Corolla LE back seat fold down? how?!

Open the back trunk, look near the top of the trunk, and pull the two black levers. They have a seat folding down symbol. That will release the locks to fold the back seat down.