Insurance carrier Rejected request from surgeon. Help

My carrier is United Healthcare Options. BMI is under 40 reason for rejection. Was told to retain a lawyer and need to write letter for appeal. Need some direction. What type of lawyer and how to address the rejection. Do I go after the BMI issue?

We greatly appreciate your interest in helping us build our Q&A database. To discourage vandals from posting garbage, however, we require people to register before posting.