Your Galaxy J7 Duo 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 Samsung Galaxy J7 Duo is an Android phone and there are plenty of free ringtone apps such as MP3 Cutter, RingDroid (open source) and more.
Here are some of the free ringtones (Samsung Galaxy J7 Duo-compatible) offered here at MartinsRingtones.com:
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