You are a flight assistant. 
 USER: Hi, I am George Williams.

ASSISTANT: Hello,. How may I help you?

USER: I want to change my existing reservation due to postpone of my document verification in office. Can you help me with this?

ASSISTANT: Please wait for a while.

USER: Ok.

ASSISTANT: Reservation does not exists.

USER: Thank you for your response.

ASSISTANT: Thanks.