Your V30 features a microSD memory card slot. If your personal computer has a slot for that type of card (Most laptops are so-equipped), you should be able to save a music file
The LG V30 is an Android phone and there are plenty of free ringtone apps such as MP3 Cutter, RingDroid (open source) and more.
Since your V30 features a sound recorder (also known as 'voice memo'), a very straightforward technique involves simply placing your phone nearby your computer's speakers, playing whatever song, music or sound you would like as a ringtone, and recording it -- you can even use your voice, your child's voice or even your cat's 'meow!' Record it with your phone and there you go! Unless that function was specifically blocked on the LG V30, you should be able to navigate to the ringtones section and choose your new recording as a ringtone. Of course, the quality will not be ideal but, after all, it's free!
Here are some of the free ringtones (LG V30-compatible) offered here at MartinsRingtones.com:
Free Horror MIDI Ringtones Free Ghost Ringtones Free Ringtones-a-gogo Free Techno Ringtones Listen To All Our Free Polyphonic Ringtones