Are you saying that you recently had performed maintenance and that you need to reset the next service reminder mileage and date?
If yes, then this
If the reminder had already been reset for you after the service, I would not mess around with it. BMWs are on conditions based servicing, meaning depending on your driving behavior the engine computer uses sensor data points and calculates how much wear is on the car and when certain maintenance items need to be replaced.
So for example, my M6 is only driven for 4,000 mi over the course of this year. At the 12-month mark, the reminder indicated I still had at least 10,000 more miles to go until the next oil change, and about 8 more months. For me I decided to change it at the 13-month mark regardless of what the indicator said, but that's just because I prefer 12-month oil changes at a minimum. After my oil change I reset the indicator and it shows the next maintenance cycle mileage and due date.
All this is an estimate, however, but I've owned a CBS BMW since 2010, and have for the most part the CBS indicators are correct.