Hi! I'm having the same problem! I ordered the hook because I saw your post. It comes with a rope, for anyone else stumbling on here with the same problem. You don't need to order that separately.
I went to the hole and tethered myself to the beach with one end of the hook. But if I jump down, I can't dive while tethered and so I can't get the atv out. And if I throw the hook right at the atv it just pulls me into the water!
How did you do it?