I was using Traktor 3.7.1 and installed 3.9 but accidentally did not import everything. What's the best way to downgrade back to the old version and then re-install 3.9?
No need for that!
Just go to the 3.71 user folder, copy everything and paste them to the 3.9 folder. Override any existed file there. :-)
If you have your Traktor Settings.tsi file you can still import them.
In Preferences you have an Import button where you will chose your file
