How to pull out the rod in a door closer by hand?

You shouldn't do that. It's very hard to pull out the rod by hand.

Instead, Install the jamb bracket, connect the door closer to it with a short pin, then hold on the tube and pull, the rod will be exposed easily.

If you must do so, you could use two small screw drivers, insert one to the hole in the rod, another at the other end of the door closer, then use your feet to hold on one, pull another one by hand.

Loosen the speed adjustment screw at other end of the door closer will speed up the return of the tube.