After replacing the brain is it required to be flashed

Personally, I think your friend is full of it. ECU replacements are done all the time.

There is no item on any vehicle called a brain box

Any testing,wiring or adapting, involving a vehicle ECU,
would require a wiring diagram & the highest level of
technical skills

The cars computer brain may be damaged now. Other than that, special code settings may be required to rest the computer brain. Never JUMP the battery using + and - posts, use the Plus + side and put the Minus - clamp on the struts, motor support mounts etc. But not on + and - posts.

hav a data stream run on car--its numbrs pinpointing the issue--partsplaces cant doit--need shop that has expensive diagnostics-not just code readers----always try reprogrammin a computer 1st-its called flashing and evn if u buy a new one-u need it done

what light flashes???

If you're really 'serious' about FIXING this vehicle, get a qualified technician to DIAGNOSE the problem. You describe an ELECTRICAL issue which requires EXPERTISE!... Since you don't have it, you NEED someone who DOES! There are NO short-cuts here regarding your issue.
The 'brain' as you call it, is the ECU (Engine Control Unit). If it has malfunctioned, this NEEDS verification/validation!.... otherwise you'll be ENDLESSLY replacing parts/components BLINDLY!
GET IT PROPERLY DIAGNOSED!

The brain is what we call ECM (computer), you need to fine out what code's he has, that the computer needs to be replace.

check all the fuses, also make sure that brain doesnt need programing,i forgot which year this started but if the brain or cluster are replaced they must be programed.

the car needs to be in the right conditions for the "brain" to run the emissions tests, the standard procedure is from a cold start, like after sitting overnight, turn all accessories off, air, radio, heat, etc.. let the car idle for 2-3 minutes, get to a highway and cruise at about 45-55 mph for 5 minutes then slow down to a stop and idle for 2 more minutes with the car in drive still, that should make the car complete the tests required to pass emissions, if that doesn't work i'd try disconnecting the battery and trying again the next day

Check your terminal connections, if they are loose they will need to be inspected for breaks. If they are broken you will need to replace the connection. Make sure they are clean and free of corrosion.

Other possible Problems
If the car wont turn over your starter could be bad.
If it turns over but wont start it could be any number of these problems.
Coil Pack
Plug Wires
Spark Plugs
EBX (Engine Brain Box)
CBX (Chassis Brain Box)
Crank Sensor
Fuel Pump
Fuel Rail
Fuel Injector

Good luck