You cannot amend the 2020 return for the wages repaid in 2021 ... it is handled on the 2021 return ...
Repayment of $3,000 or less. If the amount you repaid was $3,000 or less, deduct it from your income in the year you repaid it.
Repayment over $3,000. If the amount you repaid was more than $3,000, you can deduct the repayment. However, you can choose instead to take a tax credit for the year of repayment if you included the income under a claim of right. This means that at the time you included the income, it appeared that you had an unrestricted right to it. If you qualify for this choice, figure your tax under both methods and compare the results. Use the method (deduction or credit) that results in less tax.
See Repayments here:
https://www.irs.gov/publications/p525/ar02.html#en_US_2014_publink1000229600
What you really need to worry about is the FICA taxes that were withheld but were not refunded when you paid the excess back if you had to pay back the gross and not the net.
http://www.middlebury.edu/offices/business/tax/filing/fica_refund/node/73431#:~:text=Ask%20your%20em....
