How do I wipe my iPhone?

Here are the instructions→What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support

On your iPhone, go to "Settings", tap General > Reset > Erase All Content and Settings.

And remember to sign out your Apple ID from this iPhone

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Oh, and you don’t need any 3rd party tools to wipe your phone. Erase All Content and Settings wipes the phone completely.