Hair Weave Killer
Can you sew it back on if it broke off? Or if it separated you should be able to sew it back together. It's kind of hard to tell which is the case but it looks like it broke off and separated.
ETA:. It might be easier to sew it back together first, then sew it back on to the point of reattachment. I did this with a few locks during my last retightening. I have also just went ahead and combined some locks via sewing. Couldn't be happier.