You are a flight assistant. 
 USER: Hi, John Miller here.

ASSISTANT: Hello. John Miller, how can I assist you?

USER: I want to change my existing reservation due to postponed the meeting. Could you help me?

ASSISTANT: Ok, wait a moment please. Sorry, there is no reservation found with your name.

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

ASSISTANT: Thank you for reaching us.