How do I get the Watch App back if it was deleted?

Hi

Unless you are running iOS 10, you cannot have deleted the Watch app.

When looking for the icon manually, keep in mind that you may have moved it to a different Home screen and/or moved it into a folder (which may itself contain multiple pages of apps):

To search for the app, when viewing the Home screen on your iPhone:

Swipe down on the centre of the screen > in the Search box at the top of the screen, type "watch" > when the Watch app icon is shown, it will also show (to the right of the app icon) the name of any folder that it has been moved to.

You can also tap on the icon from within the search results to open the app:

Note that you will first need to update your iPhone to iOS 10 in order to pair and set up your watch. Be sure to make a backup of your iPhone first:

Update the iOS software on your iPhone, iPad, or iPod touch - Apple Support

If you are already using iOS 10 and have deleted the Watch app, go to the App Store > search for the app > tap on the cloud symbol to add it back to your iPhone.