How do I revert changes to the layout

You can easily revert your layout change from the Theme menu.
 

How to switch back to your previous layout:

1. On the right-hand toolbar in resume section, click Theme.
2. In the pop-up window, select the Layout tab (as shown in your screenshot).
3. Browse the available layouts and click the one you'd like to return to.
4. Once selected, click the Apply button in the bottom-right corner.