I too do not have the tab to turn off instant booking. Did you recently start an account like I did?
I just set up my account a few weeks ago. After scrolling through some other chats about this, some posted Airbnb's phone # which give you a real live peron! WOnder why you can't find that on their site.
Just got off the phone with some one this Sat am and was told that "Airbnb wants to promote instant booking" and it is NOT possible to turn it off in my case. She said she would report this to the techies or somebody and MAYBE it could be changed, I'll just have to wait and MAYBE some one will get back to me or I need to check back in. She said she totally understood my concern about having to know my schedule way in advance for certain, but she connot do anything about it at this time.
Their number is:415-800-5959
If enough people call them on this, MAYBE it will change sooner than later.
Also, go to HELP, Help Center, Feedback and give them some.