Inside the door are a couple of weld nuts - the nuts are secured to the inside of the door!
At the rear edge of the mirror's base, look for a piece of the plastic that can be pried up. Behind that secret door is a small set screw - probably allen headed. Loosen that screw and the mirror's base will release from a bracket bolted to the outside of the door. Tighten the bolts holding that bracket to the door then re-install the mirror and tighten the set screw.
At the rear edge of the mirror's base, look for a piece of the plastic that can be pried up. Behind that secret door is a small set screw - probably allen headed. Loosen that screw and the mirror's base will release from a bracket bolted to the outside of the door. Tighten the bolts holding that bracket to the door then re-install the mirror and tighten the set screw.