Prompt to Install Flash if not Detected

Hello everyone. So I recently resurrected a very old website I made using Flash. Not really knowing what I was doing (which still may be the case), I somehow sacrificed the ability to prompt the user to install the latest Flash plugin if they didn’t already have it in exchange for a full-page appearance.

So here’s the site, what do I need to add to the HTML to bring this functionality back? [link removed at author’s request]
Please note, I have a fragile ego and your criticisms may destroy me. :facepalm: