I have managed to change mileage on a Fiat 500 year 2013 successfully using OBDSTAR X300 Pro3 key programmer (same as green color OBDSTAR key master) by OBD.
Original Odometer: 74407 KM
Fiat 500 2013 Odometer Correction Procedure:
Connect X300 pro3 host with vehicle via diagnostic socket
Select Vehicles->Mileage Adjustment->Fiat->Fiat V30.64
Loading bin and initializing…
Then choose Fiat 500 model
OBDSTAR key Master is able to change mileage for Fiat, Albea, Brava, Bravo,Croma,Doblo, Ducato,Grande punto,Idea, Linea, Marelli (Auto) and others models as well.
X300 pro3 read the current mileage: 74407 KM is exactly the same as mileage displayed on dashboard.
Press ENTER button to continue
Key master tablet will ask to enter mileage you desired
Customer required to lower odometer to 59861KM
Fiat 500 mileage correction completed.