Buick 1994 Roadmaster Owner's Manual page 254

Unscrew the wingnut. From outside the vehicle,
carefully pull the taillight assembly away from the body.
Press the bulb housing release lever and turn the housing
1/4 turn counter-clockwise (to the left) to remove it.
To remove the bulb, push it in and rotate
it
counterclockwise (to the left).
Reverse all the steps to reassemble the taillight housing.