I took the screen completly off my HP Pavillion laptop and hooked up an external. I accidently told the display to read the on

Aug 30, 2018
I took the screen off my hp pavilion laptop and was using an external monitor, i accidentally told the computer to display to the on board monitor, now my external monitor wont work.Is there any keys on the key board that will undo what i did or get the external monitor to work?