If you have already filed your return, you'll need to wait for your tax return to either be rejected or accepted, if it is rejected you can add your Form W-2, correct any other errors on the return and resubmit it.
If it is accepted, you will need to amend your return to add the Form W-2.
Please see the
following TurboTax FAQ for
instructions on how to amend your tax return in TurboTax.
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