This is done by manually turning the rotor counterclockwise. If it does not move, or moves sluggishly, or doesn't snap back, your centrifugal advance is shot. Luckily ours passed the test. In A Book by Kirby Palm for guidance. In fact, if you're not in a hurry, you might want to rebuild the thing anyway.
Testing done, it's time to proceed.
The rotor pulls off. It pulls off carefully. Do not yank it. Gently wiggle it loose. You do not want to damage the shaft it mounts on.