You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I help you?

USER: I want to change my existing reservation due to some health issues, can you please help me in this?

ASSISTANT: Sure, I will help you with the change of flight reservation. May I know your name please?

USER: Thank you. Sure, my name is Benjamin Martin.

ASSISTANT: Thanks for waiting. But I am sorry to say that there is no flight reservation on your name to change it.

USER: Ok, no problem. Thank you for your service.

ASSISTANT: Thank you.