I have an LG-LS855. I don't seem to have any way to plug it in to my computer. I've made a ringtone I want to use. It's an mp3 file. I've uploaded it onto Google Drive. The only thing I seem to be able to do from my phone is play it.
I've downloaded three apps for custom ringtones. The only one that came close to helping was Tone Picker. It lets me use an mp3 from Google Drive as a ringtone. Or at least, it appears to. The phone still uses its default ringtone.
I've also figured out how to use any of the music on my phone as ringtones, but I can't figure out how to download the mp3 as music either.