I am not aware of any instructions specifically for the Siesta S6, but Pure does have instructions for another Siesta appliance. (
https://support.pure-audio.com/en-US...). It's worth a try, I think:
* Reset the radio *
Resetting the radio will erase all preset stations and restore the default presets.
1. press and hold the menu button for 3 seconds.
2. press the 'Select' button to confirm the reset; if you do not press any button, the reset will be cancelled.
Good luck