But after the extension did you file the actual 1040 return? If not why do you need to start over? You can just add the 1099 and schedule C for self employment to your return and change anything you already entered if you need to.
If you have not paid for the online edition you are using, have not filed your tax return or registered the Free edition, then you can clear your return and start over. Click on Tax Tools on the left side of the program screen while working on the 2018 online tax return. Click on Clear & Start Over.