I've just joined this site and was wondering how to apply the cinnamon to orchids for these problems and why cinnamon (what exactly does it do to help the plant)? I've never heard of this technique before.
The cinnamon dries out the tissue to prevent further infection. To the best of my knowledge, it doesn't actually kill any microbes that may be present on the tissue, so you must remove any infected tissue before applying the cinnamon (using a sharp, flame-sterilized blade). I simply put some on my finger and rub it on the wound. I disinfect my hands frequently when treating my plants for bacterial and fungal infections to prevent the infection from spreading.
As Joe said. I don't use it anymore for roots as it has been reported to stun the growth of that root. I only use it to scab wounds on leaves. I just sprinkle it on.
There are chemicals in cinnamon that act as a fungicide and as a mild bactericide, but as has been stated, the powder is better as a preventive measure than a curative one.