You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you?

USER: I am planning to change an existing reservation, due to health issue. Can you please change my reservation?

ASSISTANT: Sure, can you give me your name?

USER: I am Joshua Davis.

ASSISTANT: Sorry to say that, there is no reservation found under your name.

USER: That's fine, thank you for your service.

ASSISTANT: Thank you for using our service.