I'm probably more of a beginner, so maybe this is bad advice ^,^ ;
As I understand it, the thing you are trying to do can be solved with a bit of clever maths being used to create an offset.
But my math is weak, and I suspect that approach is better suited to more code heavy environments, so instead, This is what I would do:
Create an invisible sprite to serve as the radius, with it's origin and next image point being the distance between the two objects. Set this arm's position to the object you want to be rotated around and attach the rotating object to it's image point. Rotate the arm ( I think using Sine movement behaviour on the angle property would be the easiest way of getting this result, but I haven't tried that before.)