TL;DR
Just set up the Supervisor Password and the item will become available.
You will now be prompted for a password when entering BIOS.
You can get rid of that once you have made your changes.
Specific steps
Completely shut down your laptop.
Power on the system and as soon as the first logo screen appears, immediately press F2 to enter the BIOS.
Use the right arrow key to select Security tab.
Use the down arrow key to highlight Set Supervisor Password and press Enter.
Type some password and press Enter. Don't forget the password you enter!
Retype the password to confirm and press Enter again.
Use the right arrow key to select Boot tab.
Press the down arrow key to select Secure Boot and press Enter.
With the arrow key, highlight Disabled and press Enter.
Press the F10 key and select Yes to save the changes and exit the BIOS.