Monitor proplem

This stupid mistake of mine I was exploring the monitor and somehow I changed from d-sub port to dvi-d and it keeps telling me no signal caple connected so if anyone can help me to change it back I would be grateful
P.s it is dl2020
 
I honestly think that the answer is in the manual.
I looked up in the manual and the only way to change it is to open the menu and change it back but I cant open the menu because it doesnt open when the screen doesnt open or say no signal cabel detected
 
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