As for day tour bookings, I understand that the tours are only through Dany Island since the place is a marine sanctuary and there is a limit in place for the number of people who can go at one time.
There seem to be many random tour operators (taxi car owners) near the cruise ships but they can only go to certain places and not to others. This tour had its own buses organised. We booked in advance on the official tour on the Dany Island website https://danyisland.com/book-now/
We are looking forward to going back again. Take some snorkels if you can, and sunscreen!