How to access a post-proccess volume via script?

Hello. I am trying to access a post-process volume via script so that I can color grade a layer of blue to the screen whenever the player goes underwater. I have been trying many different references but none of them seem to be able to access the volume. My script is blank right now, as I am still trying to access the volume.

Hi!

I think that this might help:

That shows how to change bloom and vignette.

Although i dont know how to change especially color grading.