Find my phone app

From your Home Screen, swipe left until you get to the App Library at the end.

Pull downward and scroll to the Find My app or type it in the search field.

If you want to move the app out to your Home Screen, just tap/hold and drag.. it'll pop out to your Home Screen.

I'm not sure that you can turn Find My off from that app anyways if that's what you are trying to achieve. You'd go to Settings > [your name] > Find My and turn it off there.

Set up Find My on your iPhone, iPad, iPod touch, or Mac - Apple Support

Why are you planning to turn it off? Are you selling or trading in your device? If so, there is a procedure to follow..

What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support