A 2020 tax return for the SETC can no longer be filed, it had to be filed on or before May 17, 2024.
If you filed a 2021 tax return and did not include the SETC on the 2021 return you have to amend the tax return.
See this TurboTax support FAQ for amending a prior year tax return - https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-change-correct-return-a...
