Have you already filed? If so, you can't change your bank account unless your return is Rejected.
If you used TurboTax Online, and you already filed, when you Sign In, scroll down to the bottom of the page and click on 'Add a State' to get back into your return.
If you haven't filed yet, step through the FILE section and you'll be asked it you want to use the same account as last year, or 'change banks'.
@mccartney29