How to turn off find my iphone

have to turn off the find my iphone option and I cant because the screen cracked and it is not working

See >>> https://support.apple.com/en-ca/HT201441

The phrase "turn off find my phone" is not there, but removing the device from your account will turn off Find My Phone.

If you no longer have or can't access your iPhone, iPad, or iPod touch

If the steps above weren't completed and you no longer have your device, use these steps:

1. Ask the new owner to erase all content and settings using the above steps.
2. If you're using iCloud and Find My [device] on the device, sign in to iCloud.com/find or the Find My app on another device, select the device, and click Erase. After the device has been erased, click Remove from Account.
3. If you can't follow either of the above steps, change your Apple ID password. This won't remove personal information that's stored on your old device, but it prevents the new owner from deleting your information from iCloud.
4. If you're switching to a non-Apple phone, deregister iMessage. 
5. If you're using Apple Pay, you can remove your credit or debit cards at iCloud.com. Choose Account Settings to see which devices are using Apple Pay, then click the device. Next to Apple Pay, click Remove.
6. Remove your old device from your list of trusted devices.

You probably mean Find My app because Find My iPhone was there up to iOS 12. I am not clear as to what you exactly wanting to do? Why of all options disable something that will help locate your device. Something is missing here.

You can erase your device remotely using https://www.icloud.com/find but you cannot turn off Find My.