You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Stephen Lee.

ASSISTANT: How can I assist you?

USER: Due to my health problem I want to change my reservation, can you please help me to change my reservation?

ASSISTANT: Sure, please give me a minute.

USER: Ok.

ASSISTANT: Sorry, there is no reservation available on your name.

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

ASSISTANT: You are welcome.