You can access this functionality via the revisions panel which is available in the editor sidebar. Once the panel is open you will see a list of all available revisions. Each revision provides two options: preview and restore. Clicking preview will show you the entire deck from that point in time. Restore means rolling your deck back to the specified revision (all newer revisions are still kept intact so you can change your mind).
This is what it looks like when previewing a specific revision. Note that you can choose to restore either the whole presentation, or only the slide you're currently lookin at.