Wait...do you mean the Federal refund from 2020 was changed, such that the amount that you had applied to 2021 taxes changed too?
IF so, you go to the Federal Deductions&Credits page.
Scroll down the page to "Estimates and Other Taxes Paid"
expand that section
and go into "Income Taxes Paid"
in there you will find an area to go into called "2020 refund applied to 2021 Federal taxes"
that's where you change what was actually applied to 2021 taxes.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
