how to turn off find my iphone

If you want to remove Find My Phone and turn off the Activation lock, you can do that at iCloud.com/Find My Phone using a computer browser.

See the Apple Support article(s) below.

Find My Phone – Remove device.    

Use Lost Mode in Find My iPhone on iCloud.com https://support.apple.com/guide/icloud/use-lost-mode-mmfc0f0165/icloud

You need to go to iCloud, sign in and from there you can turn Find my iPhone off.