please refer to this IRS letter 2001-20
https://www.irs.gov/pub/irs-wd/01-0012.pdf
particularly this
The wages paid in error in the prior year remain taxable to the employee for that year.
This is because the employee received and had use of those funds during that year.
The employee is not entitled to file an amended return to recover the income tax on
these wages.
the following is not correct because - by taking the repayment as an itemized deduction (subject to the 2 percent floor under Code section 67). this rule was in effect only through 2018
since the repayment relates to income originally reported as self-employment income it's a business expense reported on schedule C in the year of repayment.
