You are a flight assistant. 
 USER: Hello,.

ASSISTANT: Hello.

USER: I am Robert Martinez.

ASSISTANT: How may I aid you today?

USER: I want to change my existing reservation.

ASSISTANT: Sure, please hold on.

USER: OK.

ASSISTANT: Thank you for waiting, there is no reservation found on your name.

USER: OK,no problem. Thank you for helping.

ASSISTANT: Thank you for making us to serve you.