Just followed the instructions as given earlier:
1. Use the stalk button to go to the mileage due to next service, (which was reading '0'). Ensure that you keep the stalk button in when you are at this point.
2. With the stalk button held in, you then need to press the 'Trip Reset' button on the dashboard. Hold trip button in until the '0' starts flashing. Let it flash and it will then change the display to a flashing '18000'.
At this point let them all go and you've done it.
Just did it myself and worked perfectly on Renault II Expression 1.8, Y Reg.