Download from ringtones.zone the song that you wish to be your ringtone into your Music Library. You can also save or import songs in the Apple Files app. If you skip this step you will not be able to find the song within GarageBand.
Open GarageBand. If you do not have GarageBand pre-installed on your device, you can download it in the App Store.
Import the song you want by swiping to Drums in the Tracks sections, tapping on Smart Drums and tapping on the View button followed by the Loop Browser button.
Next, select the Files tab and find the song you want to add to GarageBand using the Files app interface. Navigate to the song location in the Files app and select it.
Drag the song to the left or right to add it to GarageBand. Since the default length is extremely short you’ll need to edit the track length in order to view and hear more of your song. Hit the small + icon to add bars to your track; the more bars you add, the longer the song clip becomes.
In the editing section, you can trim the song to the desired length. The sides will turn yellow and you can pull in from the beginning or the end to create your trimmed clip. You also can loop it, split it, and more by double-tapping the song preview.
Remember that this will be a ringtone, so trim a part of the song that is appealing to the ear, and would make for a good ring whenever you get a call.
When you are finally happy with your creation, hit the drop-down arrow and tap My Songs. The ringtone you have created will automatically save as “My Song”. You can rename it by tapping on the title.
Tap and hold the thumbnail for your song and menu options will appear above. Tap the Share icon, followed by the Ringtone icon.
Name the ringtone, hit export.
When finished exporting tap Standard Ringtone to set it as the default ringtone of the device.
Now go to iPhone Settings app -> Sounds -> Ringtone and here you will see the newly create ringtone as the default ringtone of the iPhone.
These steps can be replicated numerous times. So if you wanted to create a different ringtone for each of your friends, you could do that as well.