How do i turn off the engine needs service notification on the dash of a 1988 formula firebird?

 

You've got 2 options.....

Fix/repair what-ever failed and is cuasing the 'Check Engine" light to activate.

OR

Remove the bulb from the cluster.

 

The light is on to indicate you have a problem with the engine.
The correct thing to do is to "pull the codes" to see where the problem is
Read
https://www.thirdgen.org/forums/tech...s-dumbies.html

then disconnect the battery for 30 sec for it to go away.
However if you don't fix the problem that caused the SES light ,then the light will come back on

So if you are not interested in fixing anything ,may as well just put a piece of tape over the light so you can't see it,
until your engine dies or won't start one day.