I had an instant book last week from New York City, @Joni-and-Brian0 , for the first week of July, and I just sent them links to the government (Canada and Ontario) updates. I told them it was looking unlikely the border would be open for their trip and suggested they cancel within 48 hours in order to be fully refunded. They did. They say they will rebook when the border opens, and that is fine here, as there are no shared spaces.
So that's how I am handling it, but in your case it should be even easier. You cannot send links with requests, but you could have them look those up themselves. Ask them to withdraw their request, and suggest that even if the border opens they should look for a more suitable whole-house space in which they can quarantine if that becomes a requirement.