MLR55, the light will be on due to the fault of the oil level. To switch it of without using a diag machine etc all you need to do is start the car, let it idle for a minute, switch it off, remove the keys from the ignition, open the drivers door, close the drivers door, arm the alarm, leave for a minute, disarm the alarm, open the drivers door, get in the car put the keys in the ignition, close the drivers door, start the car, let it idle for a minute then switch it off. do this a minimum of 3 times, its called "completing a drive cycle". Usually after the third complete drive cycle the fault code will be moved to a "past code" folder and after about 10 further drive cycles (just normal day to day driving) the code will be removed from the system.
All this will only work if the fault is no longer running "live".
Hope this helps
Iain