Just found my Haynes manual, here you go.
1. With the ignition turned off, press & hold the trip reset button on the right
hand side of the speedometer.
2. Ensure that all electrical items are switched off then turn the ignition switch to position 1. Do not
start the engine.
3. After 5 seconds the words 'oil service' or 'inspection' are shown with
the word 'reset' or 're'.
4. Release the button, immediately re-press and hold it. After 5 seconds the word 'reset' or 're' will start to flash.
5. Release the button, then press and release it again. The new service interval is diplayed.
6. Press & release the button one more time.
The words 'End SIA' are now displayed. Turn off the ignition.