Have you already actually filed the 2019 return to the IRS, or is it still in preparation?
Are you using Online TurboTax? If you haven't registered or filed, it should let you clear and start over.
FAQ: How do I clear and start over in Online TurboTax?
https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-clear-and-start-over-in-turbotax-onli...
If you already filed the 2019 return, then you need to explain more about what you are wanting to do. If you efiled, and it's rejected, you can make any changes and resubmit the efile. If it was accepted, however, then you can prepare a form 1040X Amended Return. We can tell you more details if that's your circumstance.
