I think that's a ring holding down the movement. It may be pulled out to disengage and free the movement but you might need to remove the screws mentined before, the 2 on the very edge (maybe at 11 and 5?). The "indentation" on the ring (12 oclock ?) is to pull it out or so it seems.
Once the ring is removed, the opening will be wide enough for the movement + dial to come out.
Again, I'm speculating here, proceed with caution.