Replacing window in Driver's door of LDV Convoy 400 series?

Window was smashed. Purchased second-hand window and now received. How do I re-fit the window please? I have managed to get the glass back into the frame, however, I cannot now remove the window to attach the riser that is attached to the window winder?

I'm now stuck with a window that will not open in the usual manner, but slips down thru gravity as it is not supported in any way. Can anyone help me please? I'd like to do this myself without having to go to a commercial van repairers if possible...