First of all, you need a BMW ID. If you do not yet have a BMW ID, follow the welcome message on your vehicle's control display. As soon as your BMW ID is registered, it is automatically added to your vehicle. If you already use the My BMW app with your BMW ID, and you log in to a BMW with it, the vehicle will also be automatically added to your garage.
As soon as your BMW is connected, you can start the registration for BMW Charging directly via the My BMW app. To do this, select the 'BMW Charging Account' tab under 'Charge here'.
You can find a how-to video on the registration process here:
Alternatively, you can register with your login details for the electric vehicle charging services via bmw-charging.com.