How do I lock my stolen iPhone 7 to avoid data breach?

"How do I lock my stolen iPhone 7 to avoid data breach?: Please I need a way to lock my iPhone 7 so that nobody can use it unless the thief return it to me"

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If a Device is Stollen...

Modify your Credentials:

Having been stolen, consider modifying your credentials, ASAP, starting with a new password.

• Modify: your login credentials (using both a New eMail and a New Password) for Apple and each and all sites
• Associate: a different method of payment to your account
• Enable: Two-Factor Authentication for Apple ID PayPal and for all other accounts that have such an applicable option

B. Verify Your Devices:

Verify that your the devices logged in to your account or still officially yours, by using this link: Check your Apple ID Device List to See where you're Signed in - Apple Support

See if your iPhone is lost permanently at Find your lost iPhone or iPad - Apple Support

Your phone is locked if you set up a Passcode on the phone. There is no way that a thief could ever guess your correct passcode in less than 10 tries.

After 10 incorrect tries, your phone will not even allow the thief to try to guess at any more passcodes.