Question: how to set a purchased song as a ringtone on iphone x?
Answer: On your iPhone X, open the Settings app;
Now scroll down to Sound & Haptics;
Once again, scroll down to the section called 'Sound and Vibration Patterns'. Tap on 'Ringtone';
Now tap on 'Tone Store';
You'll now open the iTunes Tone store where you can buy and download new ringtones.