How do I change the position of the dotted line in editor ?

I am using scale outer form my game

that means that my background has margins from both side of the screen

Can i change in the editor that the dotted line (window view) would be in the horizontal center and not on the right?

You can not change the location.

The dotted line is a representative of the window size set in the project properties.

From what your saying it sounds like your canvas is smaller then the scaled window size.

Perhaps try a bigger layout, or smaller window size.