I found a following doc. About Add a watchOS App Target to an Existing iOS Project. But I couldn't find I want info. Would you please let me know how to add an iOS Target to Existing watchOS Project?
I created project by watchApp.
https://developer.apple.com/documentation/watchkit/setting_up_a_watchos_project
Hello! You can find the target in the same way you found it from the iOS app. Press the "+" to add a target, choose "iOS", and then scroll down until you find the "Application" area (below the "Application Extension" and "Test" areas; see below). Just make sure you name the same way as your initial watchOS app. I did not see any difference in the end result when I compared it with an "iOS app with Watch App" project. Good luck with your development!