Unfortunately you can not add your 2020 unemployment income on your 2021 tax return. Each year is a separate unit. So you may need to amend your 2020 tax return. What was the amount of your 2020 Unemployment Income?
https://www.irs.gov/forms-pubs/new-exclusion-of-up-to-10200-of-unemployment-compensation
You may be able to exclude up to $10,200 of your unemployment benefits as per the above IRS article.
Also, depends what state you live in? Some of the states, not all, also tax these benefits. That means, you may need to amend federal and state both.
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