Hey, bro, hopefully this is what you want:
Mossberg 930 SBE gas piston
https://imgur.com/gallery/0IJqNm1
The factory piston uses an inner and outer ring to make the seal. The SBE piston only uses the outer ring from your factory part. A narrow bladed screwdriver can be slid into the ring gap, then twist the ring apart & over the lip of the piston. Play gently with it. Its a durable part, but expect to work it over the retaining lip of the piston, not pry it open enough to just come up.
Installation is the reverse. The main thing is to make sure you have the beveled, or cupped, edge of the gas ring facing up, as you snap it in place. When you look at it, think of it as a funnel for the gas, which is exactly what it is.
I think Steve included pretty decent instructions, when I received mine.
The last pic is my solution to the shell-dump lockup. It is the GG&G oversized button, trimmed and fit to work with the Beretta 1301 release shroud. With this combo, it is impossible to cause the shell-dump. The latch & button is ~$50, and the shroud is $9 + shipping.