The K5 Note 2018 has a microSD memory card reader. If your personal computer can also read that card type (Most notebooks are so-equipped), you should be able to save music files
The K5 Note 2018 is a smartphone. Most smartphones will let you save any mp3 song available online by touching and holding your finger on it, then selecting 'save.' Once a music file is stored on your library, tap-and-hold it and select 'assign' in the contextual menu.
The K5 Note 2018 is equipped with Bluetooth version 4.2, which lets you connect to your computer wirelessly. Just pair phone and computer together and drag and drop any music file from your computer to your Lenovo K5 Note (2018).
If the above-mentioned approaches fail or if you prefer not to buy new accessories, you can always use one of the numerous free '3G Uploader' services available online. A search on Katapulco should retrieve plenty of them. 3G uploaders are simple: Transfer your own ringtones on their web site and they will provide a URL. Navigating to that URL with your Lenovo K5 Note (2018)'s browser will download the free ringtone.
More on free ringtones
Here are links to some of the 100% free ringtones (Lenovo K5 Note (2018)-compatible) offered here at MartinsRingtones.com:
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