You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: My name is Gregory Walker.

ASSISTANT: How may I aid you today?

USER: I am planning to do some changes in my existing reservation, can you help me for that?

ASSISTANT: Sure, I am here to help you.

USER: Thank you.

ASSISTANT: Sorry, no reservation found on your name.

USER: That's ok, thank you for checking.

ASSISTANT: Welcome, have a nice day.