If you happen to swallow a small piece of metal from your braces and you're not choking on the metal from the braces then there's nothing to worry about.
Swallowing a small amount of metal from braces is not harmful to your health as long as you're not choking and eventually the stomach acid will digest tiny bits of metal.
The rest of the metal from the braces you've swallowed will just eventually move through your stomach and out through your intestines and then be pooped out.
If you're choking on the metal then get help but if not then there's nothing to worry about.
I've swallowed small pieces of metal from my braces as a teenager and nothing bad happened.
I called my dentist about it and the dentist said as long as I'm not choking then there was nothing to worry about.