@Mariana758 The guest just needs to call Airbnb and ask for a cash refund. If they booked before March 14th it should be granted - The guest just needs to check the latest Airbnb covid policies.
Even where a guest booked post March 14th I managed (at the second attempt) to persuade Airbnb to refund in full by explaining that it was legal when booked and made illegal by lockdown. It took time but they recognised this as an extenuating circumstance