I've got a BIG problem with CSS,can someone help me?

I've accidently changed the resolution of the aplication.Now,when i lauch it,my monitor remains black(as if it was turned off).I searched in the internet on how to rectify the problem and successfully found a way return it to normal resolution.I was supposed to use STEAM(for my 1st time) and change the lauch options but when i add CSS to the My Games tab,it is read as a shotcut and has no lauch options in its properties.So can someone help me to add it as an aplication(and not as a shortcut) please?