You can access your saved application by returning to the Consular Electronic Application Center (CEAC) website and selecting View/Edit from the IV and Alien Registration section of the Immigrant Visa – Summary Information screen. You will then be provided with a list of all applicants in your case along with the status of each application (NOT STARTED, INCOMPLETE, or SUBMITTED). To continue updating an incomplete application, simply click on the "Edit" button to the right of the application’s status.
Once you submit your application, by clicking the “Sign and Submit Application” button on the "Sign and Submit" page, you will be unable to access your application again without the assistance of NVC, or the U.S. embassy or consulate at which you plan to apply.