If child support or maintenance is not assigned under section 518A.81 , and an obligor has overpaid a child support or maintenance obligation because of a modification or error in the amount owed, the public authority shall:
(1) apply the amount of the overpayment to reduce the amount of any child support or maintenance-related arrearages or debts owed to the obligee; and
(2) if an overpayment exists after the reduction of any arrearage or debt, reduce the amount of the child support remitted to the obligee by an amount no greater than 20 percent of the current monthly support or maintenance obligation and remit this amount to the obligor until the overpayment is reduced to zero.