I have a method to try but your Scania P310 may need to be done with a scanner.
The method I have is as follows:
Turn the ignition to position I ensure the doors are closed.
Press the system selection button until KM or Temp reading is show in the display.
Press and hold the PHONE CALL button and immediately then press and hold the OK button, keep them held for 5 seconds.
Now press the scroll button to highlight ASSIST PLUS, then FULL SERVICE and confirm by pressing OK
Press the OK and back buttons until you have exited from the menu.
Turn off the ignition and then turn on again, the service should be reset.
If this does not work or the menus do not come up then it may not be possible without the scanner.
I do hope this helps and if it does answer you question I would appreciate it if you would click accept aand rate me.