How do I fix a rear door window in a 2001 Audi A4 that will not close?

The window will go down but not back up.How do I fix a rear door window in a 2001 Audi A4 that will not close?You are going to have to take the door panel off and check out what the problem is.happened to me in my BMW and I had to weld the metal bar that hold the window it broke.