Restarting iPhone 8
How do I factory data reset an iPhone 8 that will not rest. Whenever I do that it still has all the apps, as pictured on it.
If you go to Settings > General > Reset and then select Erase All Content and Settings and follow those prompts.. it will wipe the phone to factory settings.
What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support