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This will need to be done by the dealer. There is no way to do it otherwise.
There will likely be a 1 hour labor charge for this.
The module that controls bmw assist has other functions, so simply unhooking it will cause other issues. You will need to have it programmed out at the dealer.
Just ask them to disable bmw assist. Simple as that.
No. It's your car. You can do what you want.
This will cause other issues. Do not do this.