How do you change the hood latch cable on a 1990 Pontiac Firebird when you cannot find the answers in your repair manual?

It depends on what is wrong with the cable. When you pull the hood release within the car, is the latch not popping? If you can get the hood up at all, then you should look at the actual latch system where the cable runs, there is a metal clip that holds the cable to the latch. Have another person pull the interior latch release and watch the cable.