If you use adaptive cruise control and let the car accelerate on it's own, you will get better, but the best city MPG I have so far is about 37.
Go here, spend the day watching these videos, you will learn tons
part one
part 2
As to RESETTING the MPG, it is in settings on the screen.
On screen on left side tap on VEHICLE, then tap on TRIP INFORMATION then change from CURRENT to HISTORY then reset the MPG. (click update I believe)