There is a firing pin retaining pin (Part #5) which must be driven out. This pin is typically a "wringing fit," which means it may take a little effort to drive it out, and a little care to not mar the slide.
When you drive it out, Part #4 (firing pin spring) might go Pwoing and throw the firing pin out across the room. Disassemble it inside a large clear plastic bag, like maybe a dry cleaner's bag.
Otherwise keep a strong magnet handy to find it subsequent to the Pwoing. This is not too likely, because firing pin springs are typically pretty weak, but you never know. The magnet is used to sweep the area around the carpet under the black mark on the wall where the firing pin and/or spring hit, hopefully finding the Pwoinged parts for you.
Pwoing is a technical term used by gunsmiths here in the midwest/southwest.
The system is probably the same for both rimfire and centerfire pistols (e.g., .25 ACP), but the parts location may be slightly different, offset one way or another in the rimfire.
I betcha the firing pin broke right at the cutout in it where the retaining pin goes. Ten bucks says so.
Hope this helps.