@Merilin0
It's really easy. Follow these steps:
1.) In any web browser you go to your dashboard, once you've logged into your Airbnb account.
2.) Go to the tab "Your listings" and select the Lightning icon to turn Instant Book OFF. If the icon is yellow, then Instant Book is ON, when grey, it's OFF.
3.) Another way to turn Instant Book OFF, is selecting the listing, then in the side menu on the left go for "Booking", here you should select option "No one. Guests who meet Airbnb’s requirements must wait for your response."
4.) You can do similarly in the app on any Smart device.
Wherever you go, there you are.