How do I change the ringtone on my iPhone to one person?

How to Assign a Custom Ringtone to a Specific Contact on iPhone

1. Launch the Contacts app on your ?iPhone?.
2. Select a contact from the list.
3. Tap Edit in the top-right corner of the screen.
4. Tap Ringtone.
5. Choose one of the sounds that you want to use below Ringtones.
6. Tap Done in the top-right corner of the screen.