You'll need to open your trunk, then look carefully along the driver's side of the trunk's inner panel. The release lever is usually a small, somewhat hidden lever or button that you can push or pull.
If you can't find it, a quick online search for "1992 Lincoln Mark VII LSC fuel door release location" with images might help you pinpoint its location. You can also try searching on YouTube for a video showing the trunk area of that model car.