DISCLAIMER I have not adjusted a montero rear door, but in general the bolts that clamp the hinge to the body is loosened and the door repositioned and bolts reclamped. I say clamped b/c there is a plate that floats with the bolts inside that body panel and hence clamps the hinge into place.
A bit of lifting on the end of the door can show if it is from the hinge pins being worn.

89 v6 Raider 5spd
89 v6 Montero auto
86 TD Trooper