Here is how it works:
To select Mono or Stereo output on the Majesty, press and hold the Piezo volume knob, the signal will mute and return, and the output will alternate between mono and stereo. When the signal returns, the LED on the battery box as well as the signal will pulse once for Mono or twice for Stereo. (This "pulsing" also happens every time the instrument is plugged in, so the user knows the output setting upon startup).
The trick here is to keep holding the knob. The length time from initial press, to mute, to signal again is about 7-10 seconds, and is this long to ensure during live play, the function is not accidentally activated.
If at any time the knob is released before the signal returns, the instrument will exit the function with no changes made to the output.