How are you moving the low-cut switch? I don't see how to grab onto it.

I don't have a Sanken CS-3, but on most mics of that type, the switches are recessed to prevent accidental movement. Move the switch with a small pointy device, for instance a ball-point pen. Do not use a pencil! or something that would leave behind metallic or corrosive residue or break off in the switch.

A tip of a tiny screwdriver - like the ones used in the glasses repair kit.

Or perhaps a paper clip.

Yep and be careful of anything that's magnetised .. keep it well away from the head of the mic.

Cheers.