Your Nokia 7 Plus has a microSD memory card reader. If your personal computer can also read that card type (Most laptops are so-equipped), you should be able to save a music file
The Nokia 7 plus 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 (Nokia 7 plus-compatible) offered here at MartinsRingtones.com:
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