If you just want to make sure that heads is working, you can skip all of the security steps and make sure your system boots. To do this, simply press:
When you power on, you should see a menu informing you that a “clean boot” is detected. You can plug in your USB and follow the on-screen instructions to setup heads. If you ever want to start over, or you forgot your key(s), you can follow these steps to reset from the main menu: