Assuming you have the vent frame out? First roll the window regulator up, not all the way, just close to the top. Now you should be able to tilt the window rear edge down and back onto the roller. Once you get the glass in, roll window down to the stop, allow enough room so that you can tilt the glass back enough to slide the vent window assembly down into the door, careful not the bind up on the window. The shop manual has instructions on this procedure. Hope this helps.
