how do i remove Cupertino from apple watch screen?

On your iPhone, in the Clock app > tap the World Clock tab, then:

> Tap Edit (top left) > then remove Cupertino from your list by tapping on the minus sign next to it, then tap Done.

> Tap the plus sign (top right) > Add any cities that represent time zones you would like to add on your watch face.

Then, when customising the watch face on your Apple Watch (via firm press on watch face > tap Customize):

- Swipe left until you can select individual face features > Tap the one you’d like to use for a world clock > Turn the Digital Crown to choose a city (it offers each location that you set up on your iPhone) > When you’re finished, press the Digital Crown.

World Clock is available on these watch faces: Chronograph, Color, Mickey Mouse, Modular, Simple, and Utility (and you can add more than one on some of them).

More info here: https://help.apple.com/watch/#/apd06093d4ae