You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how may I serve you today?

USER: I need to change my existing reservation, Can you please help me with that?

ASSISTANT: Sure, may I know your name?

USER: I am David Harris.

ASSISTANT: Please wait, I will check the reservation and get back to you.

USER: Sure.

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

USER: Ok, no problem. Thanks for your information.

ASSISTANT: Thank you for reaching us.