Reset Service Display

Hi, I recently purchased a 2010 MK6 Golf 1.6 TDI. The service display was illuminated when I bought the car, so I put it into my local mechanic who completed a full service. He then attempted to reset the display, but the button on the left hand side of the dash would not work to initiate the reset. Does anyone know what would cause this button not to work, or perhaps suggest an alternative method to reset the display? Many thanks in advance.