My guess is the developer tools. Maybe the web page makes you open a date dropdown for "check-in" > select check-in date, same for checkout, hit "search", and then a pop-up would open saying "sorry, nothing available", which you'd have to dismiss before repeating the process, but in the developer tools you might be a able to see that there's an XHR query which is just something like /searchAvailability?checkIn=20230313&checkOut=20230315/&guests=2, and OP's script could just modify the dates and hit this request URL.