You could try a very old trick with thin thread (Cotton might do it) what you need is a length of thread and tie an ordinary granny knot into it BUT do not pull it tight instead leave a loop! Place the loop over the protruding screw cap cover and pull the knot tight (just enough to grip the cover) then try pulling the thread to loosen the cover, do it gently and you may need to use something to spread the effect of the thread "cutting" into your hand / fingers, a screwdriver / or even a piece of wood should do the trick.

Thanks both.
The screw covers are slightly recessed, so it looks like a digging job. I already tried a small screwdriver blade, but started to damage the cover.
I'll persevere.

Love your sense of humor