underpayment of tax

I got part way through the underpayment of tax section on TT Premier and need to recheck/possibly change some answers. When I click the back button it won't let me go back to those questions, just takes me back to the Other Tax Situations main page. Have tried multiple times. How can I go back and make changes to the questions I previously answered? And, as long as I have not filed yet, can I go back additional times? I am still not sure about some of the answers since I never had an underpayment penalty before.

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