To perform a factory reset on the base station for the SD series, first ensure that all power sources have been disconnected (both via USB and mains supply).
Wait a moment to ensure there is no residual charge left in the base station.
On the back of the base, press and hold the reset button (the small black button located near the microphone volume dial).
Whilst continuing to press the reset button, reconnect power to the base. Once power has been reconnected, you may release the reset button.
The base station should now carry out a reset.