Global Column Layout
The global column layout can be set via the customizer:
Global Layout > Column Layout. By default this controls the column layout for ALL pages. However, you’ll often want to set a different column layout on specific pages.
To do this go to the page editor screen (for the page you want to override the column layout on). Scroll down until you see the ‘Page Display Option’ meta box on the right hand side of the screen. Then, simply select the column layout you want to use for this page only from the drop down box.
Note: You can do this for posts too in exactly the same way.