@Rainbow11 the way that I found a way to do this, is go to calender, then press the dates you want to block and you will see a green "Edit" box on bottom. Press Edit and next page is "Availability" you choose Available or Block and a green "Save" box on bottom then press "Save"
. The page goes back to calender with days blocked.
I hope this helps. Just checked with google typed in How to block an Airbnb date. Came up Airbnb site "To make dates available or blocked" with steps how to do this.