As per always with this kind of thread which there now are hundreds of, if not more.
Creating a variable is not the same as instantiating an actor. A variable is just an address of an actor instance, or another name it can be known as. But which actual instance do you mean? What if there are 5? You must to tell the editor which actor instance specifically you wish the var to refer to.
Where is your actor instance, how does it make it into the game? That’s what is being mentioned above by Setting - assinging value (actor instance) to a variable.