How to view Advanced Boot Options on an external monitor?

Basically, I'm using a lenovo L420 and the screen is broken. I've connected the computer to a couple old monitors i have and it works, however, i can't view the Advanced Boot Options from the monitor and it only displays any image once I've pressed enter and windows has booted up. I just want to factory reset my computer in order to wipe the (c. Drive.

I'm computer retarded, can anyone help?

Boot options… You do not need to see the screen… You just tapping the correct keyboard key as soon as you turn the laptop on… Generally it is either f 2 or f 12…