You need to go into the iDrive system and adjust the default for the vents that the warm & cold air comes out of when you use the Auto button for the ventilation system.
Also, right next to the Auto button are other buttons to override the default flow instead to the airflow to the windshield, center vents and/or footwells.
You have the owner's manual? Detailed instructions there. Just a little reading and patience and you'll get it.
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