Can a return that has been printed be changed in turbotax? I found a long term cap gain that I neglected to put on my return and need to add it before I file the return

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/

When you sign onto your online account and land on the Tax Home web page, scroll down and click on Add a state. 

This will take you back to the 2020 online tax return so you can make the changes before the tax return is filed.

To change your return:

1. Scroll down to Your tax returns & documents.
2. Select 2020 and then select Add a state (you're not actually adding a state, this just gets you back into your return)
3. You can now add or change your info.