I mistakenly checked the wrong box on the Schedule C form. I cannot figure out how to go back and make the change. How do I do this?

At the top right of the screen, there is a "forms" button.  Click on that to change the view from "step by step" to "forms" (you can go back and forth between the two views.  Scroll down and find your form and select it, and either make your changes there or click on "step by step" which should take you to that part of the process to make your changes.