The mileage is stored in multiple places. Including the DIC. The DIC does not just display what the PCM/BCM tells it to for mileage. You will have to get it reprogrammed at the dealer. It is illegal to tamper with the mileage on a car, so you may have to go to 2 or more dealers to find one that will do it. And if some tell you that they can't do it, give them these directions and see if they will do it then.

Grand Prixs Of North America • View topic - Reprogramming DIC for Odometer reading