How to shut off find my iPhone

From the iPhone itself:

1. Tap Settings > [your name].
2. Scroll down and tap Sign Out. 
3. Enter your Apple ID password and tap Turn Off.

From online:

1. Sign in to iCloud.com with your Apple ID.
2. Go to Find My iPhone.
3. Click All Devices at the top of the screen.
4. Select the device that you want to remove from iCloud.
5. Click Erase [device]. Select Next until the device is erased. 
6. Click Remove from Account.