Hi, the reset button is where the odometer reset button is. you press it down hold it for 5 second menu will pop up on the speedometer, then each time you press it down it goes down one time. if you wanna reset it just hold for 2 second on the item and another window will pop up on the rpm clock beside the speedometer. after so many kilometers you have to change the brake sensor even if you brake pads are still good to be able to reset it again, it is stupid but that is how it is.
There is a detailed reset procedure that you have to follow once the maintenance has been performed. You need to purchase a repair manual or access to www.alldatadiy.com. You may be able to find the instructions at http://www.bimmerfest.com/ or another BMW forum.