the amount repaid in the same year as received (2020) should have been excluded from taxable income.
to get any benefit of the amount repaid in 2021 it must exceed $3,000
then you have an option
1) take as a deduction on schedule A line 16 and denote as IRC 1341 repayment
OR
2) recompute the taxes for 2020 by excluding the payment. the decrease in taxes is taken as a credit on schedule 3 line 12d denote as IRC 1341
