B&G H1000 autopilot and display how to perform a factory reset

[simondewing]

Just acquired several old B&G H1000 display units and an autopilot as the LCD screen on mine has failed (apparently a common problem).
The user manuals refer to a factory reset which removes all calibration values and resets the security PIN to 0000 but give no information on how to do this.
Does anyone have that information or experience how this reset is achieved?

Thanks

Simon