Peugeot 206 cc odometer problem?

Had a problem with the insrument pod where all readings zeroed at times. Had it tested and was told the pod was at fault. Went to the breakers and found a replacement from a vehicle that was a year older and when fitting it all the dials are now working correctly but the mileage shown on the odometer is higher than that of my original unit. How do I get the mileage back to the original number shown on my old unit.