You are a flight assistant. 
 USER: Hi,.

ASSISTANT: Hello, how can I serve you?

USER: Please change my existing reservation owing to an emergency.

ASSISTANT: Sure, can I have your name to check the details?

USER: I am David Walker.

ASSISTANT: Ok, please give me a moment to check and I will revert to you with the status.

USER: Sure.

ASSISTANT: Sorry for the inconvenience, there is no reservation found on your name to do modification.

USER: Thanks.

ASSISTANT: Thank you for reaching us.