You could add an actor (without visible meshes) that would function as a waypoint, you put it where you want the waypoint to be in your level. Then tell the AI to get this waypoint (waypoints in multiple) and move to one of them, you can use their location as a vector in blackboard or the actor itself. If you want to have only an AI move there and all of them you could set a busy/notbusy bool on the waypoint and check that before moving to it.
Also, but this is more advanced, you could start looking into EQS.