We would recommend that you completely mask off the tweeter with masking tape (Painter's masking tape). This leaves no residue and protects both the tweeter itself and the surrounding surface.
Then use a very compact screwdriver very carefully, inserting it one after the other into the holes where the screws were before.
By gently moving the screwdriver back and forth, the tweeter should loosen and, if you angle the monitor a little, gravity should assist you in loosening the tweeter.
If it still does not come off:
If you put the screwdriver into the hole and then angle it, it is then possible to use it as a handle to pull the waveguide out.
You can force gravity by knocking on the back side of the cabinet.
If this not works, it is recommended to use such a tool:
It is possible that the housing changes minimally due to the influence of different humidity conditions.
This then leads to the tweeter being somewhat more difficult to release and turn.