If you have filed your tax return and then discover that you want to add your daughter you will have to wait until the IRS either accepts or rejects your tax return.
If the return is rejected you will correct the error that caused the rejection, add your daughter and refile your return.
If the return was accepted by the IRS then you will have to file an amended tax return using Form 1040X to add your daughter to your tax return.
This link to the TurboTax Help page How to amend (change or correct) a return you already filed provides information on how to amend your tax return.
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