Sorry, I usually comment my examples but I was in a bit of a rush.
So, there are a few ways to do this. The most simple way is with a single event, something like Touch -> Is touching object | Dial -> Rotate 5 degrees toward (Touch.X, Touch.Y).
But that limits the player to having to keep their mouse/finger on the dial the whole time. I prefer to allow them to initiate the touch while on the dial, but then they can move their mouse/finger anywhere on-screen and the dial will follow the mouse/touch.
To achieve this, I used a dummy object that is created when the user touches the dial, and is destroyed when they release the touch. But the dummy object will always follow the player's finger, no matter where it goes on-screen, and the dial will always point towards the dummy object, not the finger, which means the player can move their finger wherever they want and the dial will adjust accordingly.