As long as you have not filed your return yet, you can go back to the Personal Info section to add a dependent.

How do I add or remove a dependent?

 

If you need to revisit the Dependents section in TurboTax Online, here's what you do:

1. Open or continue your return in TurboTax, if you aren't already in it.
2. Select My Info in the left navigation.
3. Select the Add a dependent button if you need to add someone. Select the trash can icon next to the name of a dependent to remove them (we'll ask you to confirm removing them before we take them off your return).

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If you already filed your return,  you cannot change or amend a return that has already been filed.  Your return will show pending until the IRS opens up their e-file system (Feb 12th).  Your return will stay on TurboTax servers until the IRS is accepting returns.  You cannot get it back, & do not make any changes to your return.  The changes would not go through. 

 

To make any changes to your return,  you will have to wait until your return gets accepted or rejected.  

 

If your return gets rejected, you can just make the changes you need to do, then you can e-file your return again.  

 

If your return gets accepted, then once your original return is fully processed, you would have to amend your return to make changes.