The 2019 amendment instructions are not functional yet ... in early December when the online system opens the amendment option will be presented.
https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed
If you used the TurboTax online editions for the 2019 tax return you will need to download the tax data file from the online account to your computer. You will need to install the 2019 TurboTax software on your computer to open the 2019 tax data file.
If you purchased one of the 2019 TurboTax online editions you can contact TurboTax support to have them push a 2019 desktop installation file to your download account at no charge - https://support.turbotax.intuit.com/contact/
