No, sorry, this is not the right place. This is a discussion forum for hosts. If your guest cancelled through the site he will be refunded 50% via airbnb. You do not need to do anything provided he cancelled within the time limit for having a 50% refund (one week prior to arrival).
Perhaps take some time to learn about how the site works and read about the different cancellation policies.
Here is a good place to start:
https://community.airbnb.com/t5/Getting-Started/Community-Help-Guides/m-p/23100#M190