how to turn off find my i phone

Review this support article, just turn it off rather than on

Set up Find My on your iPhone, Mac, AirPods, or other devices - Apple Support

note that if you lose your iPhone or it gets stolen and this setting is turned off, you won't able to use this function to assist with locating your phone.

If you are asking because you are selling/gettting rid of your phone, also review this article

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