WHOA! Wait.
Check that the locking studs are unlocked before you force anything. I don't know for sure if the 20ths have locking studs, but let's assume they do.
Take the smallest
allen wrench, and stick the long part down into the anchor post (it has a small hole down the center), and try to see if it will stick (you know, turn it to find a grip). If it does, turn it counter-clockwise to loosen it. Once done, you should be able to lower the anchor using the proper allen wrench. After lowering to your desired height, go back with the smallest wrench and turn clockwise until it stops (locking the anchor).
If your JEM is new (Edge Pro), it might not have the locking studs.