Mazda Repair: check engine light still on after repairs, blown head gasket, 2000 mazda 626

Question
I have a 2000 Mazda 626 4 cyl. 2 weeks ago, overheated. Was told that it was a blown head gasket. Replaced the head with used part.  Check engine light still own. Diagnostic says cam sensor.  Replaced with used cam sensor. Engine light still own, and diagnostic still says cam sensor. Car seems to be running fine.  My mechanic says the overheating may have damaged the car's computer.
He is now looking for used computer, to check to see if that will clear the light and code.  Didn't realize how many computers there are for that year, model.No luck Yet!
Is there a process to go through to get the computer to reset and check engine light to go off? Hate to invest the money in computer, if not needed. I am at the end of my rope.
Thanks for any help,
Mark

Answer
you need to have it scaned and the scan tool can remove the stored code and reset the computer as long as the problem was ceracted it want display the engine light but if the problem is still there the light will come on again make sure you gaped the sensor properly