You should wait until the return is either
accepted or rejected. If your return is rejected, you will be able to add the W-2 before you resubmit.
If your return is accepted, you can amend,
or correct, your return if the original entries were incomplete. There is no
additional charge to use Turbo Tax to amend your return, but you will need
to mail in the amended forms, as the IRS does not accept e-files on
amendments.
Here is a Turbo Tax FAQ with step-by-step
instructions for amending 2016.
https://ttlc.intuit.com/replies/5114064
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