Clear it. put an empty mag in. pull the slide back just enough to insert an empty case (or a fresh round if you don't have an empty), as if it were a "stovepipe", and let the slide slowly close on the case. Insert a punch in the hole on the side of the slide just above the base of the slide toward the rear. At the same time as you depress the plunger (probably a better term for it, but I can't think of one right now) through that hole, lift straight up on the rear of the slide. When the slide clears, it now moves straight forward off of the frame and barrel just as a Walther PPK, etc.
BT