the latching system is fairly simple on the third door, the handle has a cable that goes to the botom latch, and another cable that goes to the top latch.
usually if the door won't release either the cable has popped off the handle or the latch, or the latch is broken.
if you need more info just reply back.
heres an expoded view of the door.
and heres the manual instructions
atch-Rear Door, Upper
To install, reverse the removal procedure.