Your Galaxy A6 Plus 2018 has a microSD memory card slot. If your personal computer is compatible with that card type (Most laptops are so-equipped), you should be able to save a music file
The Samsung Galaxy A6+ (2018) 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 (Samsung Galaxy A6+ (2018)-compatible) offered here at MartinsRingtones.com:
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