Reset button not working on Fortigate-100F?

Hi, I have tried using the reset button during operation and also after one power cycle but the reset button is not resetting my Fortigate-100F with FortiOS 7.4.7. I have left the button pressed for more than 30 seconds but it does not make any changes. Is there a specific step I must carry out to reset my device? I have checked on the OS and admin-reset-button command is set to enable so the button should work. Please I would really appreciate your support.