Join Date: May 2005
Location: Sherwood Forest
From interpretation of the handbook (which admittedly is not straightforward)
CFG1/2/3 select the service interval. 18,600, 12,500 or 9,300 miles respectively (can be set for different usage patterns for different models).
Once you've got the CFGn displayed, a quick push on the button switches between them, but once you've got the one you want, hold the button down (it says at least 5 seconds).
This should reset the service interval to the required mileage, and reset the service indicator.
I assume you have had the service indicator switch on due to mileage? The spanner symbol on mine always displays as a test on switch on. When a service is due, I additionally expect a countdown to appear and not disappear until the config above is done.