It’s probably in the manual somewhere but Google is so much faster. The Prius Chat forum had the answer:
- Press start (ignition) button
- Make sure your odometer displays “ODO” and not “TRIP”
- Press and hold the ODO trip reset button
- Press start button to turn car off
- Press start button (again) to start car
- Hold the ODO button in until all the flashing lines on the odometer go away and the mileage returns and the “maintenance” light stops flashing