I'm fairly sure mine was all plastic. It's fairly buried now, so I think it will take a while to find.
It might be worth a look down inside with a dentists mirror or something, (My daughters always use their phones to peep in awkward places) to see if there's a hex for an Allen key in there. I couldn't comment on the metal band, so it's suck it and see I'm afraid.
Hopefully you will find that it's not that tight. It's just a very fiddly business getting the strap in place.
Good luck.
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