You haven’t shown us what the original shader and code for buoyancy looks like. Instead, you’ve asked us to watch a YouTube video, then look at your code and do the conversion for you.
We are here to help you, but we are volunteers. No one wants to have to dig through a YouTube video for details. It seems like a really nest video.
Where did the shader you like come from? (Because you clearly didn’t write it.) It also appears insanely overcomplicated for a water shader.
It might help you to read this: Posting guidelines in #Help channel