How can I file a tax form I did not know I would receive after I had already filed my taxes?

[DeniseF1 · Accepted solution]

Since you have already filed you will need to wait until the IRS either rejects or accepts your return.  If your return is rejected, you will be able to go into your account and make the necessary changes and re-submit your return.  If the IRS accepts your return, you must wait until it has been fully processed and you receive your refund or have paid your balance due. In the meanwhile, do not go in and make any changes to your return.

If your return is accepted, you will need to prepare an amended tax return and mail it in. You cannot e-file an amended return.  They have to be mailed, and it takes around 12 weeks for the IRS to process an amended return. 3 weeks after you mailed your amendment, you can start tracking its progress at the IRS Where's My Amended Return? site.

Instructions to amend your 2016 return can be found here. There is no charge to amend or correct a rejected return: 

https://ttlc.intuit.com/questions/3506561-received-a-w-2-form-after-filing