u/KaleidoscopeTrue7233

I have this castle on an island that i want to make in my survival world. I was wondering if there is a command where i can select the very bottom layer of the actual island and then it automatically goes down and out by one block until it hits the bottom of the ocean. For more clarification on what I mean, i want the part of the island that is underwater to be a gradual ascent from the bottom of the ocean, going up and in by one block until it breaches the surface while following the shape of my island until it breaches the surface of the water to see what you see in the image