How to cast to BP outside of level BP


So I have this probably simple question, but I really cannot figure it out. Here is my blueprint

My problem is, I don’t know how to get reference for the Object value in the cast to DoorBP.

Of course I have googled this, I know how to do it inside the Level Blueprint, and I know how to do it if I would be using OnOverlap event and similiar, however in this case I am just using event on Input. So please, how do I get the object reference outside of LevelBP?

What is the purpose of the Input Action interact? Is the player looking at the door? Is the player close to the door? How are we interacting? Does a widget pop up and we click the widget?

Imagine there are 10 doors. Which one do you mean? That’s what the editor is asking for - which door, how do we know that.