Remove some, or all, of your settings and files
Delete the settings on your iPhone to remove a specific set of settings without restoring your whole phone. Or, from the same place in the Settings app, reset your phone to the factory default settings. You can delete iPhone data from the phone or through iTunes using the Restore iPhone tool. If you use your phone to erase the data, choose which settings to delete; the iTunes restore process erases everything from your phone.
The information in this article covers iPhones running iOS 12. Previous versions use similar menus and procedures.
How to Reset the Settings on Your iPhone
After you back up your iPhone and decide what you want to erase, choose the correct reset option from the Reset page of the Settings app.
Always back up your iPhone before deleting settings or restoring it back to its factory default state. If something goes wrong, you can restore the data without permanently losing anything.
Open Settings > General > Reset. Tap the option that corresponds to what you want to reset on your iPhone. If any prompts are shown, follow the on-screen steps to complete them and finalize the reset.
Because the Reset All Content and Settings option resets the entire phone, you'll have to set it up again from scratch if you plan on using it after the reset.
Choose What to Reset
Pick from six options when you reset your iPhone: