'72 Duster How to I tighten the push out windows

My rear push out window mechanism is loose on the driver side. It appears to be a simple phillips screw but when I tried to tighten it the sucker wouldn't budge.

I figured I'd come ask you guys before I put the grunt to it and damaged the glass or some locking mechanism I can't see.

I think the tint guy came to the same conclusion as it's much looser now than when I dropped it off. I hope he didn't break anything. :-(