Which version of Alfresco WCM are you using ?
You will need to be logged into Alfresco WCM as as a content manager (for the given web project) or as an admin, to see the "Revert" (to snapshot version) action …
If you navigate into the web project, you will see "Recent Snapshots" for the staging sandbox, which can be opened to show a list of snapshots versions (filtered for a given time period, eg. today, last 7 days etc). You will then have the option to revert to a selected snapshot, via the "Revert" action shown against each snapshot version.
Regards,
Jan