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I am using octopi on a raspberry pi 4 2gb and a logetech C922 webcam
From what I recall, mjpg-streamer doesn't store those settings, so worst case you can reboot the entire rpi and it should go back to default.
Alternatively, the Camera Settings plugin does have a 'Restore Defaults' button. It also allows you to access those controls within OctoPrint and apply a saved preset after reboot, so you may want to check it out if you haven't seen it yet.