The IRS requests that you do Not amend your 2020 tax return at this time for the UC exclusion.
IRS statement - https://www.irs.gov/newsroom/irs-statement-american-rescue-plan-act-of-2021
For those who received unemployment benefits last year and have already filed their 2020 tax return, the IRS emphasizes they should not file an amended return at this time, until the IRS issues additional guidance.