All S-Series with sunroof
Gently but firmly pull down near a corner of the trim, then work around. The trim is snapped on near each corner (four snap points), but there is no way to remove the trim other than pulling it down or removing the whole headliner, which is very time consuming. There might be a slight risk of plastic breaking if it is very old, but it doesn’t seem likely.
Line it up and snap it in. The wider part of the trim goes toward the front of the car. Just line up the snaps, or the map light buttons, and push it up to snap it in place.