CAUTION: This is where things get dicey so be extra careful from here on out.

There are two obscured JIS-000 screws holding the PCB assembly to the knurled outer ring. Notice on the PCB on one side near the FFC connector there is a small notch in the PCB substrate. This is to allow you access to the two screws. Rotate the PCB assembly so that this notch lines up with each screw and remove them.

NOTE: You do not need to fully remove the screws yet. Just make sure they're no longer holding the PCB into the outer ring.