You cannot enter a Form 1099-G from 2020 on a 2021 tax return.
If you did not enter the 2020 Form 1099-G on your 2020 tax return then you have to amend the 2020 tax return to add the UC.
See this TurboTax support FAQ for amending a 2020 tax return - https://ttlc.intuit.com/community/amending/help/how-do-i-amend-my-return/00/27439
