@Margie20 - You cannot reissue a voucher. The guest must get this back from Airbnb. The guest is beholden to your cancellation policy (strict) for cancelling:
https://www.airbnb.com/home/cancellation_policies#strict
If you want to pay them out of your pocket for the 50% (or more) that they agreed to pay you when they booked, you can do that directly. However, I would counsel you not to do this as it is a way for them to get cash for the value of a voucher. It's laundering money and probably illegal in your country - you cannot give cash value for items given to the guest for free.
If they are eligible for a refund based on the Extenuating Circumstances policy, they need to apply for that themselves.
This is a lesson in knowing that you do not actually control the money - Airbnb does.