Since you have already paid, you cannot use the option to Clear & Start over.  If you haven't filed your return, you can go back through each section to make any changes.

If you already filed your return & it has been accepted, to make any changes you would need to amend your return.  Amended returns must be mailed.

How to amend (change or correct) a return you already filed

https://ttlc.intuit.com/community/amending/help/how-to-amend-change-or-correct-a-return-you-already-...