GN250 - have to push rear brake hard before brake light turns on

Hi all. New person here.

As the title says, my GN250's brake light works, but I have to push quite hard before it comes on.

I've done some poking around and have located the screw that needs to be twisted to tighten the spring to make the light more sensitive, but it's really, really difficult to access it. Does anyone have any tricks or know of a special tool used to turn that screw?

Thanks all

GN250 - have to push rear brake hard before brake light turns on