If you access the main TurboTax menu using the icon in the top left corner of your screen, you will see an option to access "My Tax Timeline". From there you can scroll down to view previous years tax returns.
Click on 2019 and then select "view e-file details". This should provide you with the date you filed.
As a side note: TurboTax online will most likely prompt you to upgrade to a higher version of TurboTax (ie, Deluxe, Premiere, PLUS, etc.). The reason it may require an upgrade is because you have been using the TurboTax "Federal Free" edition the past year, which does not allow you to view your previous years' tax return information. I just wanted to warn you of this in case TurboTax requires you to upgrade you are not surprised.