Make sure that you are in the same Turbo Tax account that you used previously; the following FAQ can assist in deciphering in whether you have multiple accounts: Multiple Accounts?

If you are in the appropriate account, you should be able to access your previous return by following these steps: Accessing prior year tax return

....and if you still don't see a "Documents" or "Tax Home" on the left side of the screen? 

........  Many times you need to get a couple pages into the actual 2020 file before those selections show up.

..........and even then, not every version of TTX has a "Documents" section, click on "Tax Home" instead, then scroll down the page to find the prior years to open and download:

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