I don't know where you got that idea. I typed in "How to appeal medicare coverage denial?" and found this website:
File an appeal
When someone calls a private company to account for denied coverage, it's called a civil suit. The government is infinitely more callable than a private insurance company.
If you have your health insurance from your employer and they are a large company, say more than 50 to 100 employees then most likely your company is self-insured. Who ever you think that your health care insurance company is, Wellpoint, Blue Cross-Blue Shield, Atena, etc. they aren't. Your company hires them administer the health plan but they don't have any financial interest in your care. For a fee of say 5% they collect all of the bills for the medical care of all of the employees for your company, add them up and add 5% to the total and send it to your company. When they get the payment from your company then then they pay the doctors, druggist and hospitals.
If the insurance company denies coverage just go to your boss and complain. If your company is willing to cover it then the insurance will, after all your company is paying for it. The insurance company doesn't care. In fact they will earn slightly more money, the 5% of the cost of the previously denied item.
I've seen a few situations where Employer provided coverage declined to cover a specific procedure.These were medium sized companies and had an actual group policy with the provider. The only real choice available to the employee was to sue in civil court.