Facebook game page not found, did I hide it and can I get access to it again

They keep changing how this works. Not sure if this is quite the same as what you describe - as that's never happened to me, but perhaps you might find it appears in the same place??

The latest instruction is - hover your mouse over the News Feed link at the top left and an edit icon will appear to the left of it. You can then click on that to get a list of the people, pages and apps you have hidden and can unhide them.

Unfortunately, there is currently no way to do that.

Facebook has a long history of finely restricting user options regarding what shows up in their feed- by removing previous features or options unannounced, deliberately changing user-selected preferences without the user's knowledge, and deliberately nerfing user-discovered workarounds to the limitations Facebook has imposed, even introducing features designed to give the user a slight perception of control, bundled tightly with larger changes which in fact reduce user control.

Facebook very frequently will have help and FAQ articles which are totally out of date and incorrect. Most of the time, said help articles suggest that a feature or option exists, when in reality it was deliberately removed (or removed, and re-added, and removed again, and re-added again but in a different way, and removed again).

This just is one of those various little items; it's an option which appears to give some measure of control to the user, but it's an option whose control Facebook keeps control far out of the hands of the user.