You can calculate and report the correct carryover basis on your 2024 Form 8606 and amend prior ones for support after the fact.
The Form 8606 is considered a "standalone" form. You won't need to amend your whole return for those years, just update the 8606, print, sign, and mail. You should be able to update the form within TurboTax, however you may need to download the desktop version for older years to make changes to the form.
