@Áine7 A date alteration isn't something a guest is entitled to- it has to be agreed to by the host.
When you book a place, you agree to the cancellation policy that is stated for that listing, it's a contract. The host has no obligation to waive that policy just because a guest's plans changed, one of the group got sick, etc. If there are govt. travel restrictions that prevent you from travelling, or from the host accommodating you, and you can produce documentation to Airbnb to prove that, it may be eligible for refund, but no one knows at this point what the restrictions might be for May.
Many hosts will offer to refund if you cancel so the calendar dates open up to new bookings and the host can rebook those dates, so you can ask the host about that. But they aren't under obligation to do so.