A photo is worth a 1000 woodruff keys. If there is sufficient room to work with a Dremel tool, cut the key out with a small Dremel cut off wheel being careful to not go oversize.
Constantly test fit with another replacement key.
However, the first thing you should do is consult with Mr. Google.
https://www.google.com/search?q=ho+t...hrome&ie=UTF-8