There’s no great “trade secret” as to how to reset the service indicator lamp on most Peugeot / Citroen, simply refer to pages in the Owner’s Handbook!
For reference of those interested in such matters, but who might not have access to an owner’s manual, this is the procedure to follow:
1) Ensure “ignition” key is turned off.
2) Depress and hold the odometer reset button whilst turning the “ignition” switch to the on position.
3) Keep the odometer reset button depressed for 10 seconds whilst the service display counts down from 10 to 0. When the count down reaches zero the spanner icon will vanish from the display and the service indicator will be reset.
Note 1: When reset, the service indicator is actually reset to 9,500 miles. The mileage that the car accumulates henceforth is subtracted from 9,500 miles, until 9,500 miles have elapsed at which point the service indicator icon will reappear inorder to warn the driver that the next service is imminent. Any mileage accumulated beyond 10,000 miles since the last reset will be indicated with a minus sign displayed infront of the mileage to indicate by how much a service is overdue.
Note 2: To the best of my knowledge, the above service light reset procedure applicable to most Peugeot cars, most Citroen cars and most Fiat cars with the exception of the Fiat Stilo. (Also applicable to car derrived vans from the above ranges).