If you have passed the last service mileage when you reset it will deduct this mileage from next service distance (eg over run buy 2K miles service will display 10K). A second reset will fix this and reset to 12K.
If it has the wrong interval programmed it can be changed in Planet. Not sure on 307 but on 106 and some others you could change distance for service interval by doing the following
•Switch off the ignition
•Press and Hold the daytrip meter button situated to the right/bottom of the Rev counter
•Switch on the ignition
•The display will begin a 10 second countdown.
•Release the button before the countdown finishes
•The service interval is displayed
•Each brief press of the button alternates the setting
•When the required service interval is displayed, press the button for 10 seconds to confirm.