On my Phone
Turn off Find My iPhone on the device
Click on your name at the top.
Scroll down to iCloud
Then scroll down again to Find my iPhone
Once here’s you’ll slide the toggle switch to off and enter your iCloud password.
Here’s a video for you visual learners.
Your device is no longer associated with Find My iPhone. We are now able to send your device in for service.
On a Computer
Turn off Find My iPhone with iCloud.com
If you have Two Factor Authentication on you may see this screen.
If you don’t have another device to authenticate from select find my iphone here:
Or Log in and select Find my iPhone
It will start to search for your devices.
Any devices online will show with a map, if none of your devices are online you will see this screen.
Click on the All Devices dropdown menu and choose your device (it should be offline)
You should then see this screen, Click Remove from Account
You will then see a conformation dialog box. Click Remove.