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
**Mark the post that answers your question by clicking on "Mark as Best Answer"
....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: