How i can run function from UUserWidget class using interface?

When i want use function i find actor in world and use interface funtion likr this.


But when i want find a Widget i cant do this because this not a actor.
I tried to call a function in an Actor which has a WidgetCompont in which is my BPW but I was unable to add the BPW to the WidgetCompont in C++.
Sorry for my bad English