You should first delete the original, and then import (or manually) enter the corrected 1099.

Please read this TurboTax FAQ for additional information on “How do I delete forms in TurboTax Online?”: How do I delete forms in TurboTax Online?

Please read this TurboTax FAQ for additional information about importing a Form 1099: How do I import my 1099?

You can also do a search for a 1099, and then when you land on the "Summary" page, you just click on the Garbage can icon next to the form that you want to delete.