Voigtlander Bessa RF

Does anyone have any experience of adjusting the rangefinder in a 1930's Voigtlander Bessa RF, is it possible to adjust without taking the top plate off ? I seem to remember reading somewhere it was. Or how to get the top plate off ? Any information gratefully received ! Thank you

I had one of those w/ a Heliar lens, wow, what a great camera. From what I remember, getting to the RF mechanism looked awfully difficult. I just learned to compensate for the amount it was off in the viewfinder.