Can you please tell me the best possible way to tell someone you have an eating disorder?

It depends upon: Whom you wish to tell & why you wish to tell them. You have taken the first step by acknowledging you have an eating disorder. Have you undergone evaluation to determine that? If not, then that is an important step. Then work with your physician/therapist toward effective treatment of your condition and achievement of normal eating. Best wishes in accomplishing this challenge.