You can amend if your unemployment was over the $10,200 exclusion amount or if you had withholding.
First, make sure that your 2020 return was accepted in TurboTax Online or paper-filed through the mail. You can't amend a return that hasn't been filed yet.
When you're ready to amend, find your situation below and follow the instructions.
TurboTax Online
TurboTax CD/Download