Adding liquid into glass

I’ve been wondering how it would be possible to fill the inside of this glass to make look like liquid. I already know what material/texture to use but I do not know how to add a mesh that would fill out all the creases of the inside of the glass.

maybe use a fluid simulation like

Or you could select the inside of the glass, then press ‘Shift + d’ to duplicate them, then without moving the copy press enter and then press ‘p’ to make it a different object. Then just fill the hole on top and you’ll have a perfect copy of the inside of the cup.