You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how can I help you?

USER: I am John Clark. Since my meeting in the office got postpone, please change my existing reservation.

ASSISTANT: Sure, please wait for a moment.

USER: Ok.

ASSISTANT: Thank you for waiting, I am sorry there is no reservation found with your details.

USER: That's fine, thank you for the information.

ASSISTANT: Welcome.