Hm ok.
So your button 100% needs to be clicked? You can make a Sphere Collider in the Button Blueprint and the OnOverlapBegin event could enable input. OnOverlapEnd would be used to disable input. This is just a sidenode.
Ok back to your problem. You should have a function inside your ButtonBP.
So try casting the Hit Actor to the Button Blueprint and from the return value of the cast, drag out the function and call it. It will call the function on the button you pressed.