What is it you are trying to "get back"? Only admins can edit that page so the best we can do is provide instructions. If you want to revert the navigation to a previous version, open the dropdown menu next to the edit button and click "History". This will show you all of the different versions of the page that have been saved. If you want to revert to the previous version, just click the "undo" link for the version at the top of the list and save the changes. If you want to revert to an even older version, you can either click on the timestamp for that version. This will bring you to that version of the page. Then click the edit button and save. This will save the content of the older version over the content of the current version.