The Roadster uses the centre button of the three:

• Switch on the ignition and double tap the centre button to select the service interval
• Switch the ignition off (the interval will remain in the display)
• Now before the display reverts back to current mileage, press and hold the centre button, whilst turning the ignition back on.
• Keep holding, and the display will flash, and the new service interval will display.
• You will also note, that the number of spanners will change from 1 to 2, or vice versa, indicating an A or B service.