Unfortunately, once you have gone past that point, you can no longer change your answer. You would need to start a new return if you want to change who you are preparing your return for.
To start a new return, select “Start a New Return” from under “My Returns” in the top left corner. Once you have started your new return, you can select “View All Returns” from under “My Accounts & Returns”. Then delete the unwanted return by clicking the small Trash Can next to it or “Delete” under the return’s name.