On my '92, it is a button which pops up upon impact. You simply push it back down till it clicks and stays down on its own.
The purpose of that switch is to prevent the disasters caused by a high pressure fuel leak.
If you have to push your's down as described, don't start it right away. Instead, cycle the key (every 2 seconds) between "off" and "run" a few times. Then get out and check under the car (front to rear) and under the hood for leaks. If no leaks, go ahead and start it and immediately recheck for leaks.