The procedure for the Mégane II (2002-2006, pre-facelift model) is:
Scroll through the trip computer until you get to the “change oil soon message/miles to next service” displayed.
Press and hold the mileage trip reset button on the speedo untill the display flashes, and then stays fixed. This can take a few seconds.
If you mean the spanner symbol & message such as ‘change oil soon’ just scroll through your trip computer as you do when you zero your trip mileage when you fill up with petrol.
(press top button of right hand stalk).
Scroll through trip mileage/ averages etc until you get to the change oil message and then clear it the same way you clear your trip mileage by holding the button in until the message flashes & clears.