How can I access this old Unitrends box that requires Adobe Flash to view the settings?

I hope I am not the only one who has had this trouble recently. But long story short, we were using a very old super ancient Unitrends for our backups. We use it in a very limited capacity now for a couple of servers that are 99% no longer in use, but for those few situations where we still need to keep the backups running. It was running fine the last couple of years, but just this week we noticed an alert stating, "Inventory full sync completed with 1 warning(s)" and it looks like the past several days the backup that runs daily is failing. I went to our old admin server with IE11 installed that we typically use for older systems that require compatibility mode, but of course Flash is no longer available in IE11 and compatibility mode is not working. Tried downloading Firefox ESR but that also does not have flash. Best I can tell is I might need to try downloading flash from an online source, but I am not sure who to trust. I did try plugging directly into the Unitriends, and it just has a page that states to navigate to the web interface to manage it with the IP address. So kind of stuck in a catch-22 here. I've seen some suggestions online to use virtual box to create a Windows 7 machine and try connecting with the built in flash that way, but it seems pretty excessive to have to go this route, plus I dont' want anything that unsecure touching the network so I'd likely have to patch it or create a seperate tunnel or something before I am comfortable putting it on the live network. Anyone else have a suggestion?