You can refund the guest from the Stripe dashboard.

Since the service is settled for 100 USD and a fee of 3.2USD (2.9% + 0.03 USD) is charged, 96.8 USD will be credited to the host.

If you refund 100 USD to the guest, the host is responsible for the difference between the 3.2USD (2.9% + 0.03 USD).