Where is the fuel door release solenoid on a 1995 buick riviera

If it is electronic and not manual, there is probably a fuse in the fuse box, a switch somewhere and an actuator at the fuel door itself. start all electronic problem diagnostics by checking the fuses and relays associated with the component that is not working.

I agree ^^^^. However inside the trunk, upper left is a release handle in which to open the gas opening.

The solenoid is behind the fuel door and the release. Pry the two plastic keepers out with a screw driver and the solenoid will pull out the fuel door opening.