I am surprised there is no DIY for this in the sticky.
waiting for TP...my memory is shot.
I think you pull it forward a bit, then you insert a small flathead screwdriver...either in the front or rear of the top portion...then it comes off.
ok, got it. thanks. under the cover is a metal "barrel". looks a bit like a gun barrel, with the "sight end" at the back side away from the button. the little clip on the cover snaps over the "sight notch".
so just a slide of a very small common screwdriver does the trick.