Aedgington, after looking at mine, there should be a Philips screw drawing the window onto the mount/operator. It’s tight against the window on mine, but I would not give it death, as this could break the glass. You probably should use some removable Loctite 242 to prevent this form reoccurring.
I didn’t have to do mine; I just looked at it to help you out. The black button is not a button, but the back of the bolt going through the glass with a rubber grommet. Open the window and try accessing it form the inside. If you cannot get to it from inside, then use a #2 Philips apex bit with a ratcheting screwdriver. Snap-on model R810SA works well. Sorry I didn’t look any further.
Hope this helps.