how do you reset the maintanance milage?

Your owners manual with answer this but I too will give it a try. With the maintenance code up on you dash display, doors closed and the igniation in the II spot, push and hold the same button you use to reset your trip odometer. For this you have to hold for 10 seconds or slightly longer. Once it starts flashing let go and press and hold again for 5 seconds or longer. It will then reset to 100%