The Form 1040X is currently scheduled to be released on 2/27/2020. Please see the TurboTax FAQ: IRS forms availability table for TurboTax individual (personal) tax products to track the upcoming release date.
For information on how to Amend your 2019 return once the form is available, please see the TurboTax FAQ: How do I amend my 2019 TurboTax Online return?