Hello and welcome to our Forum
Unfortunately, when you work in BMW Ecu, it cannot be modified or adjusted without a diagnostic scanner, the more new cars the more they rely on functions in Scan tools.
As I know, for old BMW cars you may adjust the DME idle speed by some adjustment screw (sometimes a plate) located on/near the TPS.
Now one of our BMW engineers is working on releasing some useful information about how to adjust the idle speed in BMW engines
Please wait for more 1 day, we will post the information here.