Voigtländer Bessamatic: remove the small screw cap on the left of the viewfinder.

Hello, I am in France and I have a very nice copy of Voigtländer Bessamatic "luxury". The cell ( the light meter ) seems relatively preserved: it seems to underexpose a little, but does not indicate anything as is often the case.
I know that you can access a light meter needle adjustment screw by removing the small cap to the left of the viewfinder, but how do you unscrew it?
If I succeed, is it please possible to slightly correct the position of the needle as one can do on a kyiv 4 ?

Thanks in avance...