You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you?

USER: I want to change an existing reservation, can you please help me?

ASSISTANT: Sure, I can do that for you. Please wait, let me check your reservation status first. For checking, may I know your name?

USER: Sure, I am Rachel Walker.

ASSISTANT: Sorry Walker, I have not found any reservation by your name in our database.

USER: No problem. Thank you for your information.

ASSISTANT: You are most welcome and thank you for choosing us.