How do I repair Driver's Side Rear Window? Won't go all the way up.

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When I pressed the button to put the driver's side rear window down, I heard a loud clunk, which ended up being the window falling all the way down into the door. Thankfully, it didn't break. We're pretty knowledgeable about how to fix things, took the door panel off and got to the inside. Is this able to be fixed since it will go part way up with the button or do we have to replace a part. I'm hoping we can fix as oppose to replace! Any information would be appreciated! Thank You!