im assuming your talking about the little spanner on your lcd screen??
to reset, turn the key to the ON position but do not start the car and hold the trip-meter reset button in for 10 seconds. After 10 seconds, release the button and turn the key off.
note - trip-meter will display zero while button is held in.
p.s. this is for AU's so im pretty confident it'd work for EF's aswell.
hope this helps