Form 1040X is scheduled to be available on TurboTax on 2/7/19.
If your return got accepted by the IRS, you'll have to amend your income tax return(s) to add additional W-2's or 1099's.
However, the IRS has not finalized the 1040X amendment ELECTRONIC form yet. They're scheduled to issue that form around February 14, 2019. When they do issue the form, see How to amend (change or correct) a return you already filed.
Related information:
· Can I amend if I already received my refund?
· Do I need to amend my state if I amend my federal?
· IRS Forms Availability Table for TurboTax Individual (Personal) Tax Products
· State Forms Availability Table for TurboTax Individual (Personal) Tax Products