Did you already file the return and need to amend it to add the 1099?
If you have not filed yet then click on Add a State to let you back in to your return to continue.
Enter a 1099-Int under
Federal
Wages & Income
Interest and Dividends
Interest on 1099-INT - Click the Start or Update button
Don't try to import it. On the Let Us Enter Your 1099 page scroll down to the bottom and pick Enter a different way
