Solved
Help documents say there should be an option to downgrade once you get to the File part of TurboTax, but this option does not exist. Using Downgrade from the side menu is greyed out even though I did not use the help of any experts throughout preparing my tax return.
An update and resolution:
Unfortunately, the option to switch to "Do It Yourself" is not available online. Starting over does nothing but forces me to start in Expert Assist, with no option to choose/upgrade/downgrade a different product (except Full Service). There is no explanation as to why Do It Yourself is not available. I also haven't touched any Expert Assist functions so the option to switch to Do It Yourself should be available.
In the end I had to call TurboTax and have them offer me a resolution to the situation since the website and online help documentation was of no help and/or inaccurate.
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