Overpayment letter from the unemployment office - first time posting

After 21 weeks of benefits I got a notice saying I must repay some of it. I worked as a welding apprentice before this. The letter mentions an appeal window and a repayment plan. Who should I talk to first?

Thanks for writing this out. I went through something close to it last year, and it got easier once I kept a simple log of every call and form.