I received a 1099 from the IRS I didn’t know about and need to add it to my taxes

If you have already submitted your tax return, you will have to wait until Feb 12 when the IRS opens the gate. You cannot return to the program to make any changes before that. 

If your return got rejected for whatever reasons, you can return to the program / account to add the Form 1099 along with other changes.  You do not need an amendment 1040-X.

If your return has been accepted, you will have to amend your return by filing a form 1040X.  You should not try to amend your return until it has been fully processed and you have received your refund or your payment has cleared.

Beginning with the 2019 tax year, you can e-file amended tax returns. If you used TurboTax to prepare Form 1040-X, follow the software's instructions to e-file the amendment.

To see how to amend your taxes, click here: 

Steps to amend in TurboTax

How to file amendment