How do I change a 1099 to a corrected 1099 if my return has not been filed?

You can delete the old one and enter the new one.

Here are the steps for deleting unwanted forms in TurboTax Online:

Open your return in TurboTax. (To do this, sign in to TurboTax, and select the Take me to my return button.)

In the left side bar, select Tax Tools> Tools.

In the pop-up window Tool Center, choose Delete a form.

Select Delete next to the form/schedule/worksheet and follow the onscreen instructions.