Is there a way to rename cities in Civilization 6?
City Renaming has been added with the Fall 2016 update:
Open the city details pane (the highlighted page icon on the panel) and click on the city name in the top left corner of the screen
http://steamcommunity.com/app/289070/discussions/0/340412122411024672/
Apparently it's an issue they'll fix in an upcoming patch.