As I remember, on start overlap check can be problem, but if for you will be enough check collision sphere or cube, try something like this:
This is documented here https://docs.unrealengine.com/latest/INT/Gameplay/HowTo/UseRaycasts/Blueprints/
My blueprint is only one of possibilities, but should work on start too.
edited
This is simplest way and tested with sphere tracing:
You can test with print string what is “overlapped”. With print string on Out Hit you will have colliding component/actor name