Hi, my name is Paul and I will try to assist you
Mercedes digital dash's are only designed for a new unit to be installed and the mileage transferred using Mercedes STAR diagnostic tool - once the mileage is set the dash is lockedto the car and there is no way for a dealer to adjust this mileage
If you have fitted a second hand instrument cluster then this is the problem you are faced with - the car knows that this is the incorrect unit
There are specialist "mileage correction" companies that may be able to help - this is not something that we would do or use in a dealer as we would only fit a new unit for fresh coding.
Here is once such company - I would recommend searching for a company local to you and asking if they can recode your units mileage:
Mileage Correction Company
Best regards, Paul