How to erase all content and settings
If you’re concerned someone may have had physical access to your device and tampered with its built-in security, you can restore the device to its factory settings — even if you aren’t using the latest version of iOS, iPadOS and macOS. A factory restore erases the information and settings on your device. This includes removing any apps that were installed without your knowledge and resetting your privacy settings so you aren’t sharing location with any people or apps. It also installs the latest version of the operating system.
This process, known as Erase All Content and Settings, requires internet access and can take some time; however, it helps ensure that your device can be accessed only by you.
Important: When you use Erase All Content and Settings, all your data is erased.
If you want to use Erase All Content and Settings on your Mac, you must be using macOS 12.0.1 or later. Alternatively, you can erase your Mac. See the Apple Support articles Use Disk Utility to erase a Mac with Apple silicon and Use Disk Utility to erase an Intel-based Mac.
Find out how: To view a task below, select the plus button 
next to its title.
Erase your iPhone or iPad and restore it to factory settings
Go to Settings
> General > Reset, then tap Erase All Content and Settings.
Enter your passcode or Apple ID password.
Wait for all content to be safely removed from your device.
Erase your Mac and restore it to factory settings
Do one of the following:
On your Mac using macOS 13 or later: Choose Apple menu
> System Settings, click General 
, click Transfer or Reset, then click Erase All Content and Settings.On your Mac using macOS 12 or earlier: Choose Apple menu
> System Preferences, then in the menu bar, choose System Preferences > Erase All Content and Settings.
In Erase Assistant, enter your administrator information (the password you use to log in to your Mac).
Review items that will be removed in addition to your content and settings.
If your Mac has multiple user accounts, click the arrow next to your account name to review the items.
Click Continue, then follow the onscreen instructions.