How do you disengage the passenger air bag in a 1991 corvette?

You can't disengage the passenger-side airbag in a 1991 Corvette. There was no passenger-side airbag disable switch in that model year. The passenger airbag system was not sophisticated enough to allow for deactivation. If you need to transport a child in a rear-facing car seat, you'll need to place the child in the back seat.