I don't understand your responses. Are you saying that he received the sick pay in 2016, and repaid part of it in 2020 and part in 2021? If that's the case, how much did he repay in 2020 and how much in 2021? Please give exact amounts.
Was the sick pay reported as taxable income on his 2016 tax return? Which box of his 2016 W-2 was the sick pay in?
Why do you say that he owes "a pretty large amount in taxes as of right now" because of the overpayment? What year's tax return(s) are you preparing now? The overpayment in 2016 would not increase his tax in any other year.
Please note that when you post a reply there is no indication of what you are replying to. If you give very brief or one-word responses, we can't tell what earlier post you are referring to.
