What is the treatment for crank sore?

Canker sore: This is usually a manifestation of a recurrent herpes virus infection. Though not curable, it can be controlled with medication if needed. Speak to your doctor about the options available.

Canker sore: If you meant canker sores, the typical treatment I have recommended is warm salt water rinses with liquid antihistamine mixed together. You can even dab some liquid antihistamine on the sore and experience relief. There is also a numbing paste (something like anebesol) which you can put on to protect from worsening. Get plenty of rest and hydration too.