You cannot change the information or tax refund on the original 2020 federal tax return that was filed with the IRS.
To change information you would have to complete an amended tax return, Form 1040-X, and enter on the amended return the changes made by the IRS on the original return which caused the tax refund to be reduced. The amended return would NOT be filed, it would be used for your information only.
If you PROMISE to save a PDF and a .taxfile of the original return for future use and safekeeping then you can use the amendment process to see what the return will look like after the IRS changes it for the unemployment exclusion. However if you then find a new credit was added that was not on the original return you will need redo the amendment and file/mail it AFTER you eventually get the corrected refund from the IRS. Do not jump the gun.
Remember to note the AGI on the original return so you have it to file the 2021 return ... if you amend then the program will carry over the incorrect AGI so you need to have it at hand.