In addition to being able to set a ringtone when creating a new alarm time, we can also navigate to the Clock app settings on the OnePlus smartphone and set a desired alarm tone there.

Besides the pre-installed tones, we can also set our own ringtones or mp3 files.

Android 10 | OxygenOS 10.0
Alarm sound -  Open the  Clock app
Alarm sound -  Open the  Settings
Alarm sound -  Tap on  Alarm Ringtone
Alarm sound -  Choose a  ringtone
  1. Open the Clock app
  2. Open the Settings
  3. Tap on Alarm Ringtone
  4. Choose a ringtone

OnePlus Instructions