Call support for your Geographic area

 Call support in your Geographic area with the units serial number and register password and what language you would want authorized if  other than what original owner has.They check to make sure unit isn't reported stolen and might call original owner, perform the changes on their end , however .I think the tablet has to still be within it's update period for you to do anything on your end since it likely  involve doing a factory reset ,select language,  connect to the internet , set up the tablet with your primary email , and download all the software over again, and that is not possible if it doesn't have a current update subscription.

 I would ask if support is able to do anything remotely through quick support app and Team Viewer without a need to do a factory reset to the tablet, and downloading all the software again. You might have to install a SD card for additional storage space to get BMW to install correctly