Making a variable instance editable means that the said variable will now be publicly editable on the instance of that Blueprint. Now what you will want to do is that set the default value of the said Boolean to False. And add a Sphere collider to the Light Blueprint, whenever player overlaps with it, it should set the Boolean to true and then you can make another logic based on that if the Boolean is true, then the light should turn on.
Try it by yourself, if you still can’t get it to work then let me know, I will post blueprint images for you later.