You can amend the 2020 tax return you filed using the TurboTax 2020 desktop edition.
A 2020 amended tax return can only be printed and mailed, it cannot be e-filed.
See this TurboTax support FAQ for amending a 2020 tax return originally completed and filed using TurboTax - https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-2020-return/L3XdA1Pw8_U...
