TundraTalk lists the following 2 methods, supposedly one is in the Owners Manual as well.
1. Make sure when you turn off the engine the odometer is in the regular total mileage mode. Not "a" or "b"
2. Push and hold down the mileage reset button while turning the key to the on position. (keep holding it down)
3. You will see a count down of five lines go down to zero and it will reset.
The other method:
1. put the odometer in the A mode
2. hold the re-set button down with the key in the acc position and then turn the key to the on position while still holding the button down
3. after about 5 seconds the maint reqd light will go off.