You do it with the reset button or something like that. It's in your manual but since I'm feeling extra generous tonight I went through the trouble of finding it for you:
To reset the oil monitoring system to 100% after each oil change perform the following:
1. Press the SETUP control to access the System Check function.
2. Press and releast the RESET control to display "OIL LIFE XX% HOLD RESET NEW".
3. Press and hold the RESET control for 2 seconds to display "IF NEW OIL HOLD RESET".
4. Press and hold the RESET control to display OIL LIFE SET TO 100%. Your oil life is now reset.
