@Sandra0,
there is not a lot you can do at this point.
The person who made the 2-day Instant Booking has a confirmed reservation, and it would be very bad for you to do a host cancellation. (Plus doing a host cancellation would block you from renting out those 2 days on Airbnb. You could then rent them out on VRBO, I guess. But Airbnb does not look kindly on renting out your listing to Airbnb guests using any service but Airbnb.)
Going forward, if you have an Airbnb Inquiry, you are able to "soft" block those days on the calendar. In the past, blocking days in response to an inquiry used to prevent anyone from trying to book them. Now, a block done for an Inquiry leaves the days available, but only prevents Instant Bookings (so you get the chance to review multiple requests.)
So going forward, you might want to take advantage of that feature.