The self-certifying has nothing to do with amending returns. That is just to certify with the payer for future paycheck.
Yes, you can amend prior years to correct your tax returns. But most likely tax years 2021 and earlier are past the date you can get refunds.
https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-change-correct-return-a...
