The attachment... Does it look like a pencil eraser? Or does it look like a tiny umbilical cord?
If it looks like a pencil eraser that's probably a slightly open navel. Take EXTREME care to keep that chick clean until it heals up.
If it looks like a tiny umbilical cord DO NOT PULL IT. Take some clean scissors (wipe them with alcohol first) and snip it, but not tooo close to the chick. Clip it close enough that the chick won't trip on it, and that other chicks won't try to eat it thinking it's a worm. It is, essentially, an umbilical cord.
If it doesn't look like an umbilical cord OR a pencil eraser, then we really do need a picture to help you further.