Move the scanner head a little away form its resting position. Again, by turning the gears.

Unscrew the the phillips screws at the sides of the head.

The head also has about 6 metal clips in total in the two sides. You have to undo 2 to open it for sure. But I undid all, just to be sure.

The part shown with the green circle, needed some fiddling to also undo. There are wires here, so pay attention not to damage anything! I just moved it off to the side while cleaning the mirrors.