Help Modifying City Settle Ability for New Civ

[Ethereal Storm]

Hi all, so I got inspired to create a new civilization and would love some help creating part of its civilization ability that lets them settle cities on ocean and coastal tiles. I looked into the data files for the base game to see if I could find the code I was looking for, but I'm having trouble finding it. The closest thing I could find was in the Operations file of the base game and had a target for settle location, but I couldn't find any code that specifies what a settle location is. I would love some help with this. Thanks y'all