There’s a Revisions item on the right side of the editing area if Page is chosen at the top of the right column. Once clicked you’ll get a page with a slider at the top to roll back to previous versions. This is a somewhat confusing interface, but if you exercise caution you can get to the spot you want in the timeline. Chances are you’ll simply need to step back to the previous revision. Click the Restore This Revision button near the top right of this area. Then Publish when you return back to the page.