See this TurboTax support FAQ for transferring the 2020 tax data file to the 2021 TurboTax for windows desktop edition - https://ttlc.intuit.com/community/entering-importing/help/transfer-last-year-s-return-to-turbotax-for-windows/00/26145
If you completed the 2020 tax return using the TurboTax online editions -
To access your 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 section Your tax returns & documents. Click on the Year and Click on Download .tax file
If you used the desktop CD/Download editions installed on your computer, the only copy of your tax data file and any PDF's will be on the computer where the return was created. TurboTax does not store online any returns completed using the desktop editions.