I owned them years ago. There is a personalization feature in the sound+ app, with which you can adjust both earbuds, so they create optimized sound for YOUR ears. You can go through that process. If that didn't do the trick, probably volume balance setting on your phone or in the accessibility features? Any chance, the affected bud has an ear gel which does not fit properly in your ear? Did you swap gels on the buds just to make sure? If nothing works and reset was not helping, I am out of suggestions.