I've done this once. The string is wrapped around the tongue. Your going to have to have someone help you hold her down. You will have to cut the string off of her tongue. I have no idea how they get it wrapped around the tongue, but I am pretty sure it's around your birds tongue.
You'll need some very small scissors and some steady hands. It took me about 2 hours to get the string off. They wind it around very tightly and it takes time to get up in under the string to be able to cut it loose.
i recently had a older hen to do the same thing and i just gently pulled it out. everyonce in awhile it seemed like it was kinda hanging up and i just kept the tension on it and it would turn loose and some more would come out , until it was all the way out. the hen is fine now and doing real good.