Not sure why people couldnt figure out how to customize cities....

I tried out the app and did not find customizing the cities difficult at all. You just go to settings, and you can customize your cities under "City of Weather Widget" and "City of AQI Widget". Swipe left on the city you dont want (The exact same sweeping motion you do with other Apple menus). I deleted the default ones and added my own within seconds.

St1St2St3St4 about MyWeather - 15-Day Forecast, v1.0.1