You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you?

USER: I want to make some changes in my existing reservation because I did not get the concert tickets, so I am planning to travel on another date. Can you please help me?

ASSISTANT: Sure, could you please mention your name?

USER: My name is Gary Lee.

ASSISTANT: Gary, please wait for a moment.

USER: Ok.

ASSISTANT: Sorry Gary, there is no reservation found on your name to change your reservation.

USER: Oh' It's ok, no problem. Thank you for your information.

ASSISTANT: You are welcome.