Set the fork lower in a vise (use a rag around the lower or soft Aluminum jaws to avoid gouging the fork). Use an air impact at the same time pull on the fork slider to extend it fully. The other way is to buy a tool that slides down and holds the damper rod to prevent it from spinning in the fork (item #9 in your diagram). Using the impact method, pulling the fork completely extended, put friction on the damper rod so it resists spinning, and the impact shocks the bolt loose too fast to overcome the friction.
If you have soft jaws for your vise, you can do it like I usually do, clamp the slider in the vise, and pull on the lower, while hitting it with the impact gun.