You don't "upload" it ... you OPEN it.
How to amend (change or correct) a return you already filed
You can amend e-filed returns if they've been accepted; paper-filed returns may be amended once they've been mailed.
Select your tax year for amending instructions:
@Critter-3 That FAQ is not correct to amend a 2019 online return. Goes to amend a 2020 online return. Reported to Moderators
ok...wrong word. it won't open
Did you download the 2019 tax data file which has a file extension of .tax2019?
To access your current or prior year online tax returns sign onto the TurboTax website with the User ID you used to create the account - https://myturbotax.intuit.com/
Scroll down to the bottom of the screen and on the section Your tax returns & documents click on Show. Click on the Year and Click on Download .tax file
With the 2019 amend program started, click on File in the upper left of the desktop program screen. Click on Open Tax Return. Browse to the location where you downloaded the tax data file (NOT the PDF).