Hi Richard,

Do the following:

1. Start engine.
2. Repeatedly press the trip button on the right of the clocks until "Trip A" is displayed (this may be slightly different depending on whether your car has the multifunction display or not).
3. Switch ignition off - that's an important step.
4. Press and hold the same button.
5. Switch ignition on.
6. Continue to hold the button until the display indicates "000000" and the light that looks like a spanner (if present) goes out.
7. Switch ignition off.