Your HTC Desire 12 Plus has a microSD memory card slot. If your personal computer has a slot for that card type (Most laptops are so-equipped), you should be able to save a music file
The HTC Desire 12+ is an Android phone and there are plenty of free ringtone apps such as MP3 Cutter, RingDroid (open source) and more.
More on free ringtones
Here are some of the 100% free ringtones (HTC Desire 12+-compatible) offered here at MartinsRingtones.com:
Free 'Unclassified' Ringtones Free Ghost Ringtones Free Ringtones-a-gogo Free Techno Ringtones Listen To All Our Free Polyphonic Ringtones