You can view your configuration change history in two places in Ambari Web: on the Dashboard page, Config History tab, and on each service page's Configs tab.

The Dashboard > Config History tab shows a table of all versions across all services, with each version number and the date and time the version was created. You can also see which user authored the change, and any notes about the change. Using this table, you can filter, sort, and search across versions:

The Service > Configs tab shows you only the most recent configuration change, although you can use the version scrollbar to see earlier versions. Using this tab enables you to quickly access the most recent changes to a service configuration:

Using this view, you can click any version in the scrollbar to view it, and hover your cursor over it to display an option menu that enables you to compare versions and perform a revert operation, which makes any config version that you select the current version.