You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you?

USER: I want to change my existing reservation due to some health issue. Can you help me?

ASSISTANT: Sure, may I know your good name please?

USER: Sure, I am Charles Walker.

ASSISTANT: Ok Walker, please be on hold.

USER: Ok.

ASSISTANT: Walker, there is no reservation found under your name to do changes in that.

USER: That's fine, no problem. Thank you for your time.

ASSISTANT: Thank you for choosing us.