How do you fix a 1982 Camaro that is losing horsepower?

The horse power loss you are experiencing could have many sources.

To address this:

Do a good tune up. ( a Haynes or Chilton manual has a good set of instructions)

Check the back pressure in the exhaust.

If it still down on power you may have a worn out cam shaft, this is quite common in these engines. (again the manual will have good instructions)

Good luck