Remove all the panels on the vertical surfaces of the dash front, and the covering over the door arm/hinge.
If you're lucky, one of the bolts/pins has dropped out of the linkage.
Some of the covers over the defroster motors and duct work can be removed...
A mirror and a flashlight are important tools for searching for the bits that dropped down "behind there".
Be very careful that your fingers don't get crushed while working on this. An assistant or the wind moves the door at the wrong time and you loose a finger.
Happy coaching!
Buswarrior