How do you tighten a passenger side mirror on a 1992 jeep wrangler?

if i assume correctly your talking about the mirror itself and not the part that connects to the vehicle.

If its the mirror look underneath next to the rubber part (bendie) you should see two screws on either side. Take a Phillip screwdriver and tighten it to the desired torque. Dont tighten too much tho as you could damage. Personally i have mine pretty tight so the wind doesnt have too much play on them.