You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello,. Any assistance required?

USER: I would like to change my reservation due to postpone of my sister's engagement. Please help me with it.

ASSISTANT: May I know your name?

USER: I am Gregory Walker.

ASSISTANT: Please wait for a while.

USER: Sure.

ASSISTANT: No reservation exists by name Gregory Walker.

USER: Ok, thanks for the information.

ASSISTANT: Thanks.