Step 1: Insert your key into the ignition but don't turn it.
Step 2: Press and hold down the 000 button on your odometer.
Step 3: While still holding the button, switch on your ignition.
Step 4: Keep the button pressed until you see a spanner symbol appear on the dashboard, then release it.
Step 5: Your service light should now be reset.
Note: This method may not work on all Citroen Nemo models, so it's best to consult your vehicle's manual for the exact procedure.