Add ringtones to your device
Your device comes with a set of system sounds. You can add your own ringtones by putting audio files in the ringtones folder on your device (learn how). These file types are listed: MP3, WAV, OGG, M4A, AAC, FLAC, and WMA.
Files in that folder appear under My ringtones in the tone list. To use one, see Select a file from the ringtones folder as a ringtone.
Checked against the LuneOS code and installed apps. Nobody has tried these steps by hand yet, so tell us if something differs.