How can you run Apple Diagnostic through an external monitor? My MacBook Pro A1708 is recovering from water damage.

From not working it has since been cleaned and have the LVDs Cable replaced.

Currently the display is showing black but I am able to connect to an external display.

If possible I would like to run Apple Diagnostics through an external monitor if anyone can help?
Follow these steps exactly:


Start your computer with external screen plugged in and an external keyboard, typically a USB keyboard
Once your screen is started, close its lid, it will go to sleep
On your USB keyboard, type a key. It will wake up, but now using external display as its main display
Instruct it to restart
Hold D on external keyboard when it chimes