I had this same exact issue, David. CA glue releases fumes which fogged it up, so I ended up wet-sanding it with super fine (3000 grit) sand paper until it was fairly clear. After that, I used the Novus scratch removal paste to get it clear. https://www.ebay.com/p/Novus-1-2-3-Plastic-Polish-Set-Scratch-Remover-Cleaner/1231451712?iid=400082797682
It probably seems like a waste of money to buy the Novus set rather than buy a new lens, but it sure comes in handy for armor as well.
I ended up attaching it using plain old Elmer's glue around the edges, applied with a toothpick. Dries clear, holds great.