Hi
To search for the Music 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 "music" > if the app icon is found and 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.
Under iOS 10, you may have removed the app from your iPhone. If so, to add it back:
Open the App Store app, search for "music" and add Apple's Music app back to your iPhone.