Hiya mogget,
There are a handful of "hidden menus" that can be accessed through the MMCS screen (if you have one).
These are used by the dealer to set service reminders, re-align your camera lines, etc.
If you don't have an MMCS there will be some arcane combination of switch settings that will give you access to that function via the main dashboard...
Hopefully someone with a service manual can give you more info.
That function, you've described, puts up a reminder of the next service, every time you start the car.
(The dealer showed me how to get to the hidden menus on the MMCS, but I've never needed to change them, so have forgotten the buttons to press)