The guy in this vid is kind of lost as to how to disassemble the striker once he gets it out (pull down on spring, remove 2 keepers like on a cyl head valve), but he does show how to get the striker out easily around 1:30. You push the white plastic part of the striker forward to release end cap, allowing it to slide up.
Recommend you place the slide inside a rag when you slide up the plastic end cap so you don't launch the extractor spring across the room. He didn't and you can see it bounce around on his workbench.
YouTube - Lightening the trigger pull on my SIGMA
p.s. the extractor can pop out once you have the spring and it's rod out, so watch out for small parts growing legs.