Oppo
Change Alarm Volume auf Oppo
Every alarm on your Oppo phone shares one volume level. ColorOS controls this through a single slider in the sound settings, not through a separate value for each alarm entry.
Open Settings ➔ Sound & vibration and locate the Alarm volume slider. Drag it to the level you want; the change applies immediately to every alarm you have set, including alarms you create afterward.
This setting is separate from ringtone and notification volume, so raising media or ringer volume will not make your alarms louder. If an alarm still stays silent after you raise this slider, check whether Do Not Disturb or a Focus mode is active, since some Focus profiles mute alarms regardless of the volume setting.
ColorOS has no built-in option to give individual alarms different volumes. If you need one alarm louder than another, a third-party alarm app with per-alarm volume control is the only practical workaround.