The 2020 SETC is no longer available since the 2020 return or amended 2020 return with the credit had to be filed on or before May 17,2024.
The 2021 SETC is still available. If you filed a 2021 return and were eligible for and did not claim the credit then you will have to file an amended tax return.
Go to this IRS website for information - https://www.irs.gov/newsroom/tax-credits-for-paid-leave-under-the-american-rescue-plan-act-of-2021-s...
If you used TurboTax to file the 2021 tax return then 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...
