Get a MuseLSL stream running then you can run neurofeedback.py to record EEG to a csv file.
Just an example script from the MuseLSL repo that I modified to record delta waves and save all readings to a csv file.
Note: I actually had to remake the additions to the script since I deleted my copy at some point and had never uploaded it anywhere. This script should but not necessarily will work. If it doesn't work, file an issue and I'll get to it. I don't like Python and just want to get this over with.