How do I detect a specific overlap event?

Hi Sean!
i am trying to create a side scroller game where camera stops scrolling if character enters a certain area. i created a blueprint with only collider in it, and i used OnBeginActorOverlap on 3rdPersonCharacter blueprint (got it from example map) that if it touches with collieder, camera detaches from parent and stops moving. i am using example map that is present in unreal, and player start is where player spawns as in picture.

However, i want to add multiple actors that do different things when character overlaps them, so i am using what answer is, but i can only see default tab on 3rdPerson controller blueprint. not on GameStart, as in screenshot. when i press play, i get an error message of accessed none.