When you need to make all externally linked Data-Blocks local to your Blend file in one click:
From the 3D View Object menu select Make Local > All
In the 3D View, Press L and select All
Unreal Engine 4.18
A direct reference to another actor instance can’t be created from within the blueprint because it can only be provided at run-time after the instances have been created, both the current actor and the other actor we want to refer to.
In the Actor Blueprint:
In the Map Editor: