Prepare the Ringtone: If you wish to use a custom ringtone on your iPhone, you'll need to create or download it first. Reputable websites offer free iPhone ringtones, or you can create one from a song in your music library using iTunes or a third-party app.
Connect Your iPhone to iTunes: Use a USB cable to connect your iPhone to your computer. Open iTunes on your computer if it doesn't open automatically.
Add the Ringtone to iTunes: Click on the device icon in iTunes to access your iPhone's summary page. In the left sidebar, click on "Tones" under "On My Device." Drag and drop your custom ringtone file into the "Tones" section in iTunes.
Sync the Ringtone to Your iPhone: Click "Sync" or "Apply" in iTunes to transfer the ringtone to your iPhone.
Set the Ringtone: On your iPhone, go to the "Settings" app. Navigate to "Sounds & Haptics" and tap on "Ringtone." Your custom ringtone should appear at the top of the list under "Ringtones." Tap on it to set it as your default ringtone.