ExifTool is a fantastic free software which allows changing EXIF information of multiple file types, including Cinema DNG (digital negative).
I personally use this tool to correct a faulty black level in the Digital Bolex D16 output files (in CinemaDNG format).
Download and install ExifTool for your operating system — it's available for both Windows, macOS and Linux.
Navigate to the folder containing the sequence of DNG images and type the following:
First, find out in which group BlackLevel is stored:
exiftool -G1 -blacklevel image.dng
Once you figure out where the group BlackLevel is stored, you can ask ExifTool to correct it for you.
This is the command to correct the blacklevels and exposure of Digital Bolex D16 CinemaDNG files:
exiftool -IFD0:BlackLevel=30 -BaselineExposure=0.76 *.dng
In order to overwrite the original files (which most of us probably want to do anyway), just add "-overwrite_original" to the command, like so:
exiftool -IFD0:BlackLevel=30 -BaselineExposure=0.76 -overwrite_original *.dng
Leave a comment if you have any questions!