The dealer who sold you the car has to fix it. I would guess at a poor earth connection. It's worth looking at the obvious. Make sure the battery earth cable is properly attached to the body of the car. Look under the bonnet for any detached cables. Garages are stupid these days and rely solely on electronic interrogation rather than look for the obvious. But if the poor connection is internal to the dash display it will be very hard to find and fix and they may have to fit a new instrument head unit.