Generally speaking, you can't edit a published app. You can override this using security rules but it's not recommended to do so.
To edit the app, you duplicate it, then edit the duplicated copy in your Work stream, then re-publish the app.
If you're trying to edit a sheet you created in the published app ("My sheets") and then shared to Community, for example, you wouldn't duplicate the app. Rather, you would temporarily un-publish the sheet, edit it, and re-publish the sheet. If you both Publish and Approve the sheet, though, it should become part of the app and be available in the duplicated copy.
