I'm not sure what you're asking here.
I've never used the online produce, (and never will if I can help it), but I'll describe what happens in the desktop world and assume something similar occurs in the online realm.
Until you actually file your income tax return, either e-file it or print it for mailing, you can go back to any interview in TurboTax and make changes - additions, deletions, corrections, etc. Once you're happy with the sate of your income tax return, you file it.
If you have filed your income tax return then, when you start TurboTax, instead of simply clicking on you tax file you click on the "Amend a filed return" button. That brings up an "amend" interview where the program "knows" it's going to generate a Form 1040X. The interview asks some questions about what needs to be changed - I think it just hits a few items where amending is common - but after that you are free to go anywhere in the original TurboTax interview covering any subject and make your changes = additions, deletions, etc. When you signal to TurboTax that you're done TurboTax prepares a Form 1040X, along with every other Form and Schedule that went into your original "as filed" income tax return. You send in the Form 1040X along with any Forms or Schedules that have changed.from your original filing.
