Unreal 4.17.2
The idea is very simple:
The opening angle is -90°, we easily change the direction if we mutiply it -1 or 1.
The first way is to create the required variable in c++ and call it with a getter method in the blueprint.
The second way is a little bit easier.
We create the Door direction variable in the engine.
I hope it will help someone.
Good luck!