You have two options you could use.
- You could make that variable public and allow the modification of it from anywhere.
- You could create a function which is doing that. (I would suggest this).
Now on the events “event on begin overlap” or “event hit” you get the actor which is colliding. Cast that one to your character pawn (Just go in the context menu and search for “cast to”) and then use the result of that to call that function or get/set that variable.
Will this get you started?