The K8 2018 features a microSD memory card reader. If your personal computer can also read that type of card (Most notebooks are so-equipped), you should be able to save music files
The K8 2018 is a smartphone. Most smart phones let you save any mp3 song available online by touching and holding your finger on it, then selecting 'save.' Once the music file is stored on your library, tap-and-hold it and select 'assign' in the contextual menu.
The LG K8 (2018) is an Android phone and there are plenty of free ringtone apps such as MP3 Cutter, Zedge and more.
Since your K8 2018 has a sound recorder (also known as 'voice memo'), a very simple technique involves simply placing your phone near 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 K8 (2018), you should be able to navigate to the ringtones menu and choose your new recording as a ringtone. Of course, the quality may not be ideal but, after all, it's free!
Here are links to some of the free ringtones (LG K8 (2018)-compatible) offered here at MartinsRingtones.com:
Free Horror MIDI Ringtones Free Tropical Ringtones Free Ringtones-a-gogo Free Techno Ringtones Listen To All Our Free Polyphonic Ringtones