The phrase "cog icon" refers to a small visual symbol that represents a gear or cogwheel. It is commonly used in technology or user interfaces as a symbol for settings or options. Full definition
With others you head to Settings > Apps and then hit the settings cog icon in the top corner where you'll then options to change default apps. (pocket-lint.com)
To access: swipe down from the top of the home screen > hit the settings cog icon > tap Home Screen Style > choose between Standard and App Drawer options. (pocket-lint.com)
To access swipe down from the top of the home screen > hit the settings cog icon > tap Home Screen Style (visible within first page) > choose between Standard and App Drawer options. (pocket-lint.com)