it's out of the shell but has a little string still attached. It has no more blood coming from it. should I detach the string?
Yay! Just leave it and it should dry up and come off itself. It happens with ones that need help because they don't get to rotate all the way round like they would do as they unzip which is what usually detatches them from the shell.
It's not easy, I know! Leave the humidity and if your brooder is nice and toasty you can pop it in there when it's almost dry. How's baby looking? It may need some time to rest.