[Rubbond]

If it's a knob attached by a grub screw it seems to me it will be whatever
it's trying to turn that is stiff and needs fixing.
I can't imagine an electrical switch could become stiff.
Maybe it's a remote knob working through a Bowden cable which needs greasing
or replacing? A dried out Bowden (especially if there is a kink in it) can
become very stiff, even with a push-pull movement.
Rgds,
Andy.