Using GarageBand

[AccessShell]

I am trying to make a ringtone from a downloaded m4r file. The file was converted from mp3 using an online conversion. I can see and play the file on the phone. To make this a ringtone, I use GarageBand. I need to find the file in the "My Songs" dropdown in GarageBand.
I don't know how to get the file into "My Songs"

Thanks