Answers for "react native ios simulator step one install xcode"

react native run ios on specific simulator

npx react-native run-ios --simulator="iPhone SE (1st generation)"
# list devices
xcrun simctl list devices

react native run ios runing the app in simulator not in Iphone

react-native run-ios --device

this is for connected devices


react-native run-ios --simulator="simulator name"

or 

react-native run-ios --simulator