Take the OPPO R9S mobile phone as an example. The method of setting the ringtone is as follows:

1. Open the phone, find the "Settings" item on the desktop and click to enter.

2. After entering the settings, select the "Sound and Vibration" option.

3. Then choose to set the mobile phone ringtone. Here, take China Telecom 1 phone ringtone as an example, click to enter.

4. After entering, you can choose the system ringtone, or you can choose a custom ringtone and an online ringtone. Here we take the custom ringtone as an example.

5. After entering, select the music you want to set as ringtone.