Hi @Jo44, you may not be able to turn it off. New hosts are not always given the option. I suggest putting the listing on snooze until you set your parameters, work it all out etc. You may get a booking any second now and you must try to avoid cancelling at any cost, there are penalties for doing so.
There is a very ill-thought through pilot that forces some new hosts to have IB turned on all the time. It means you have zero opportunity to have any exchange with potential guests, and increases the risk to you and your property.
Clearly from AirBnB's perspective it is a revenue generator as it encourages impulse bookings, but for hosts it is a disaster at times, and in particular for new hosts.