The W-2c does not affect your 2021 tax return at all.
If box 4 is the only change on the W-2c, it does not affect your 2020 tax return unless you had more than one employer in 2020. If you had only one employer in 2020 you do not have to do anything with the W-2c.
If you had more than one employer in 2020, the W-2c does not affect your tax return unless the total amount of Social Security tax withheld from all jobs in 2020 is more than $8,537.40. Add up the amount in box 4 of all your 2020 W-2s, using the corrected amount on the W-2c for that job. If the total is $8,537.40 or less, do not file an amended return. If the total is more than $8,537.40, you had excess Social Security tax withheld, and the increase on the W-2c produced or increased the excess. You should file an amended return to get a refund of the added excess Social Security tax withheld.
If you filed as married filing jointly for 2020, add up only the box 4 amounts for the person who got the W-2c. Do not include the other person's W-2s.
