The key is to use a tool, like snap ring pliers or fine needle-nose pliers, that can go into both holes and turn together. It's very difficult to apply the needed torque by engaging a single hole only. You may need to use moderate heat to soften the glue, if present.
I removed mine, with just a pair of needle-nose pliers. No heat was required, but there was a small, audible "snap" when the retaining ring released.
The plastic retaining ring is quite soft, so use care, as it can be easily damaged during removal. Use care when re-installing too - the threads are very easy to mess up.
With luck, they are actually sending an entire tailcap, not just the switch board.
- Syncytial.