How to file prior year amendments

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-already-filed/L4VjJ9BA2_US_en_US?uid=ld1n99kr

Which years?

If you have a number of them, you should consult with a tax professional, particularly if there is tax due.

You will no longer be able to e-file with TurboTax and will have to use a desktop (installed) version; print and mail the returns. TurboTax tax supports tax years 2020-2023 currently.

See https://turbotax.intuit.com/personal-taxes/past-years-products/