Sit behind the wheel and turn the ignition key to 'on' position - but don't start the car. Check to be sure the odometer mileage is showing and not the trip mileage. Next - turn the ignition key off. Now hold the trip / odometer reset switch down and turn the ignition to 'on'. You should see a few dashes (--- ) counting down indicating it's being reset. Then you should see the odometer reading. It's that easy.
Hope this helps. I've had to do this numerous times as the dealer techs never seem to remember to do it.