MKI - day trip reset button (next to the mileage display)
MKII - day trip reset button - indicator stalk.
Press it and turn ignition on holding it. Hold it for a 2-3 seconds and release it. There will be a new sign on your mileage display. Keep pressing reset button till you get to one with "DTC" - read codes is you can (4 digit).
BTW - where are you from?