How to change a passed reservation and refund

[Eve7]

Hi, i have a guest inquiry on 5 April for 2nights 11-13 April. I send pre-approve on 5 April for 2nights request and reservation confirmed on 6 April with 3nights because guest change the reservation date to 14 April. He did informed me that he 'might' check out 1day earlier which is 13 April when he confirm the reservation. But he only confirmed me he will earlier check out on the day he check in which is 11 April. My cancellation policy stated moderate. He say he did change the reservation date in airbnb but it still remain the same. I not sure when he change it. So is the 1day reservation refundable?if yes, how to make refund to him? Please advise. Thank you very much! 🙂