You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I assist you today?

USER: I want to change my existing reservation due to my travelling dates has been changed. Can you help me out?

ASSISTANT: Sure, may I know your name please?

USER: My name is Gregory Miller.

ASSISTANT: Sorry to say that, no reservation was found on your name.

USER: Ok, No issues.

ASSISTANT: Thank you for choosing us.

USER: Thanks for the information.