You can not add the form to your original tax return once it has been filed AND accepted by the IRS. If it gets rejected, however, just log back in to your tax return add the form and make any other necessary corrections.
If accepted, you will need to file an amended return (1040X)
to show the additional W-2. You should not try to amend your return until the original
return it has been fully processed and you have received your refund or your
payment has cleared.
Amended returns do not “catch up” to your original return
and replace them; they are processed as two separate returns.
Amended returns have to be printed and filed by mail. It can take the IRS up to 12 weeks or longer
to process them. If you are due a
larger refund than on your original return, your amended return should only
show the difference and you will receive a separate check for it. If you owe money on your amended return, it
will show only the new amount owed, you will have to mail a check with the
Click here for the 1040X: https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed