Balda Super Baldax font lens removal

Hello!

I need to remove the Balda Super Baldax (http://adopteunboitierphoto.fabien-nguyen.fr/galerie.html?page=balda_super_baldax) front lens to access the shutter blades.
I removed the outer ring, on which the lens info is engraved. It looks like the front lens is on a screw path but I don't know how to unscrew it but by using a pencil eraser.

Any tip?

Regards

Since it's a folder, you can find the locknut on the back of the shutter assy on the lens board that has 2 notches on the retaining nut. You just need something to put in there and unscrew the whole lens and shutter assy, that should make working on the shutter so much easier.