I accidentally used w-2 from 2020 instead of 2021 on my tax return, how would I go about fixing this?

[PattiF]

If your return has been filed and you were notified that it was accepted by the IRS, you will have to amend your return using Form 1040-X. If your return is rejected for some reason, you will be able to fix the error and use the correct W-2 for the tax year 2021. 

Form 1040-X is not ready from the IRS to use to amend your return. Here is a link to use when the form is ready.

You can check the availability of the form here.