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.