Good news. Becuase the gross wage repayment was greater than $3,000 you are entitled to relief under IRC 1341. The general tax rules state that if the repayment is in a different year than the receipt, wages (box 1) are not adjusted but you are entitled to a refund of any social security and medicare taxes you paid on the gross repayment. Some employers will handle this for you by reducing the repayment by the amount of these taxes others make you file form 843 to claim the refund from the iRS.
Since only boxes 3 through 6 were changed you do not file an amended return.
Your options for recouping the income taxes you paid on the gross repayment are:
1) as a 2023 deduction on schedule A line 16 denote as IRC 1341 repayment OR
2) recompute the taxes in the year you received the payment by excluding the gross repayment from box 1.
The decrease in taxes is taken as a credit on schedule 3 line 13b for 2023.
