Watch app icon disappeared but watch and phone are connectef
Apple Watch icon disappeared
Question marked as
From your Home Screen, swipe left until you get to the App Library.
Swipe downward and you'll get an alphabetical list of your apps.
Locate the app in the list or type the app name into the search field
Once you've located the Watch app, tap/hold then drag it and it'll pop out to your Home Screen
Organize the Home Screen and App Library on your iPhone - Apple Support