You should have filed a 2021 tax return for your self-employment income. The SECT can only be credited on the 2021 return, so if you filed a 2021 return you will have to amend the return that was filed to enter the credit.
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...
Go to this IRS website for information on the 2021 SETC - https://www.irs.gov/newsroom/tax-credits-for-paid-leave-under-the-american-rescue-plan-act-of-2021-s...
