Cancel reservation and refund

[Regina10]

Good evening, 

I have a guest who selected 1 room in my apartment and then decided to book another of my rooms (in the same apartment). 

Given it's a change in rooms, I agreed she would get a full refund but I don't know how to do it. I tried going to the reservation information and I see she has canceled already but the "refund button" doesn't show. 

Can you please help? 

Thanks

Regina