The thing is that you need an access from the Actor to the Level Blueprint, but the Level Blueprint, as far as I know, isn’t accessible from wherever.
There is a workaround based on Event Dispatchers. Go to Your widget and add Event Dispatcher and call it, for example, MyEvent. Then simply call it when pressed the button:
In the Level Blueprint right after you create widget (RollerHUD here) bind the other event that will do what you want:
But I’m not sure if this is what You want.
I suggest to use GameMode for any global methods and events. You can have an access to the GameMode by simply using Get Game Mode and casting it to Your GameMode.