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Tap out #22. This will allow the spring and detent to release (24 & 25). The button (21) will then simply pull out.
I would highly recommend getting the DMW oversize safety button when doing this. It can be difficult to get the assembly back together without damaging the detent spring. You have to compress the spring and detent into the trigger group, then tap the pin #22 back into place.
On my first attempt, I damaged the first coil of the spring when trying to tap the retention pin in. This came to my advantage though. I always felt that the M4's safety was too difficult to push. So I trimmed off the damaged coil. This made moving the safety much more responsive. It isn't weak by any means, I just don't have to press it with a lot of force like before. I feel Benelli did a poor job designing this part of the M4. There isn't a tool that can be bought that would assist in this task. It would have to be constructed. Imagine a very small pickle fork that would fit around the sides of the retention pin as you tap it in.
I ended up using a very small punch to hold the spring down as I tapped in the pin. This job would probably be much easier with a second person and a vice.