In your running Mac Band-in-a-Box 2017 click " loops " and then in the bottom left hand corner go " Open Folder " . If you first hoover your mouse over Open Folder it will describe what strange world ( Don't be frightened.
) that will open for you.
I don't see a folder to add it.
Create your own folder of your own loops. I named mine as MY LOOPS.
And have fun looping!
Hope i understood your question correctly.