To re-cock the striker, grab the striker end piece, pull back a little, and rotate clockwise (or rotate the bolt handle counterclockwise) until the striker is in the cocked position. While you can grab the striker with your hands, I would recommend grabbing grabbing it with a rag, since if it snaps back into position with your hand in the way it will hurt.

As for the headspace adjustment, I tried that with my bolt, and the only thing you get is a bolt that has to be rotated back to position to be inserted into the receiver; no change in headspace. What makes you think you have a cracked firing pin?