You should be able to return to the FILE portion of your TurboTax interview. Go through the entire section again, looking for the page that asks you how you'd like to pay your taxes. The interview should allow you to change the method of payment when you get to that screen.
*** I am NOT a tax expert. I am a seasoned TurboTax user, and volunteer to provide assistance to TT users. Nothing I post is to be considered TAX ADVICE; I bear no legal liability for responses.***