If my doctor put inaccurate information into my medical file which resulted in a denial of an insurance claim, how can I correct it? 

If the doctor provided inaccurate information in your medical file, you may be able to sue him, possibly in malpractice (if it was due to incompetence) or possibly in fraud (if it was deliberate; e.g. if he somehow benefitted from your denial). You would need an attorney for a lawsuit like that--suing doctors is usually fairly involved and expensive, since you can bet the doctor will have an attorney defending him. Also, all you can sue for monetarily is any actual losses you've suffered to date, so if you have not had any large out of pocket medical expenses for which you were not covered by insurance, there's little monetary recovery to offset the cost of a lawsuit. (You can also sue for an order forcing him to correct incorrect information.)

Is it possible it was an innocent mistake--that you mispoke or he misheard or both? Have you spoken with the doctor and explained to him that this was in error? If you haven't yet, you should try--he may be more than willing to correct the file and help you out.