Oppo
Set a Custom Ringtone auf Oppo
On Oppo phones running ColorOS, the ringtone option sits under the sound settings, not inside a dedicated media app. This is why many users cannot find a way to assign their own audio file, even though the feature has always been available.
The system also treats dual SIM devices differently. Each SIM slot has its own ringtone slot, so changing one does not automatically update the other. If calls on your second SIM still use the default tone, check that you selected the correct SIM before picking a file.
To set a custom ringtone, go to Tap on Settings ➔ Tap on Sound & vibration ➔ Tap on Ringtone ➔ Choose a SIM card (Dual SIM) ➔ Tap on Select from files ➔ Set a Custom ringtone.
The file does not need to sit in a specific folder. The file picker can browse your entire internal storage, so downloads, recordings, or transferred music all work as long as the format is a standard audio file.
If the ringtone still does not play after saving, check that the correct SIM card was selected in the step above, since the setting only applies to the one you picked.