Overpayment letter from the unemployment office (Honolulu)

After 13 weeks of benefits I got a notice saying I must repay some of it. I have read a lot of threads here and could not find my exact situation. The letter mentions an appeal window and a repayment plan. Who should I talk to first?

Collect your pay stubs and certification records for the weeks they name. Mine showed the error was a date mix-up.