I've had this happen with cichlids a few times, usually the loser after two males have been sparring over a female. In most of those cases it was a dislocated jaw and I was able to gently work it back into place. It held every time that I can remember except once, with a Cyprichromis sp. I tried a couple times and decided I wasn't gonna keep trying after the third time it popped out and so euthanized the fish. In that case I suspect the jaw might actually have been broken. But these were all medium to large cichlids at least 4" long.
I had this happen to a danio or tetra once years ago, it may have been a white cloud. Anyways, the problem corrected itself after a few days so you may want to wait before doing anything too drastic.
If you can see something caught in the jaw, throat or gills, I suppose you could try to extract it with small tweezers. With such a small fish it would be a delicate procedure. Personally if I saw something stuck in the mouth or gills of something that small I would euthanize it after a few days if it didn't correct itself.
These days I'm not sure I'd even try to restore a dislocated jaw on something so small, as my hands are too shaky and my fine motor skills never quite returned completely after my stroke. I'm not sure I would have even tried before that. I'd still do it on a larger cichlid or catfish, though.
In the end be careful of the fish. Trying to fix the problem could potentially be worse than the cure, or could cause damage that won't be noticeable right away but could cause the little guy to be in more pain than if you did nothing.
WYite