Make sure to check on ‘CSS Classes’ in Screen Options((Figure:1)
Add the class navbar-apply to the CSS Classes field for the menu item that you want to align right(Figure:2)
Save the menu.
By default, the Right Aligned Menu item has an orange(#EB513A ) background colour, if you would like to have the blue(#0055b7) background colour add the class navbar-alt-blue after the main class separated with a space.
Figure 1: Screen Options at the top of the menu page (Appearance > menus)