To factory reset a Mac Mini, follow these steps:

1. Turn off your Mac Mini.
2. Hold down the Command + R keys while turning on your Mac Mini. Keep holding the keys until you see the Apple logo.
3. When you see the Utilities window, select “Disk Utility” and click “Continue.”
4. In Disk Utility, select your startup disk (usually named “Macintosh HD”) and click the “Erase” button.
5. In the “Format” menu, select “Mac OS Extended (Journaled),” and then click “Erase.”
6. Exit Disk Utility and return to the Utilities window.
7. Select “Reinstall macOS” and click “Continue.”
8. Follow the on-screen instructions to complete the reinstallation process.

Note: Factory resetting your Mac Mini will erase all data, including your personal files and settings. Be sure to back up your data before starting the reset process.