Here is the easy steps to read BMW CAS3 ISN by using CGDI Prog BMW MSV80 key programmer via OBD.
Connect CGDI Prog key programmer with laptop and vehicle (shown as picture below)
Open CGDI Prog software on desktop
Select BMW Read DME ISN function
Click on Read CAS ISN
Please remove the key from the ignition
The CAS ISN data was read successfully.