In your first pic, unscrewing that metal ring removes the driver board.

I'm no flashlight guru, so I had to improvise and fashion a tool. Basically, I just use 2 allen wrenches that fit snug inside the 2 little holes. I'll clamp them between a pair of long nose vice grips and twist the ring.

As I recall, my ring was installed with some thread lock from the manufacturer. So, it's important to get a good "bite" inside the 2 ring holes for the first removal.

Hope that helps and GL!