You should be able to rotate the arm using the ATC REV button. You'll need help as it may drop both tools. Depending on exactly where in the cycle it stopped, you can also use the ATC FWD button to get the tools away from the spindle or pot.
See the two silver dowels that stick up out of the arm, close to the pivot? They are spring loaded and if you push them down, it unlocks the little clamps that clamp the tool into the arm. One clear of the spindle and pot, you can push those dowels down and remove both tools from the arm.