How do I set the world clock on the iwatch to a default city?

My world clock on my paired Iphone originally had Las Vegas as the first time zone and that is what is on my iwatch clock face. I wanted to change that to another city so I deleted Las Vegas and I added London. I then went into the iwatch app on the phone thinking that would update the default city on the watch. Nothing changed and Las Vegas still shows up on the iwatch even though Las Vegas was deleted from my world clock on my iphone. How do you change that?