The V30 Plus is a smartphone. Most smartphones will let you save any song found online by tapping and holding your finger on it, then selecting 'save.' Once a music file is saved to your media library, tap-and-hold it and select 'assign' from the drop-down menu.
The LG V30 Plus is an Android phone and there are plenty of free ringtone apps such as MP3 Cutter, RingDroid (open source) and more.
Since your V30 Plus features a sound recorder (also known as 'voice memo'), a very simple technique involves just putting 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 mobile and there you go! Unless that function was specifically blocked on the LG V30 Plus, 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 optimal but, after all, it's free!
More on free ringtones
Here are some of the 100% free ringtones (LG V30 Plus-compatible) offered here at MartinsRingtones.com:
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