the extractor is really not connected to the gun except by pressure put on the rear end of it by part #3 and the spring in the drawing. It should nearly fall out once tension is removed from it by pulling the decocker lever.
In other words, the spring, and the small pieces on each end, and their tension, are the only thing holding the extractor in place. Easy to lose.
#3 can only be oriented one way on reassembly or the extractor wont be held captive, but with the lever removed out of the way all those parts should remove easily and slide out with the spring, from the channel the spring lays in.