The TurboTax online editions are Only for tax year 2020.
To complete and file a 2019 tax return using TurboTax you would need to purchase, download and install on a personal computer one of the 2019 desktop editions from this website - https://turbotax.intuit.com/personal-taxes/past-years-products/
A 2019 tax return can only be printed and mailed, it cannot be e-filed.
Since you are filing a late 2019 return, the IRS will not have a 2019 AGI in the system for you. When the 2020 software asks for your 2019 AGI so that you can e-file 2020, use “zero.” If you cannot e-file by using zero then you will have to print, sign and mail your 2020 return.