You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: My name is Donald Brown.

ASSISTANT: How can I help full to you?

USER: I would like to change my existing reservation to some other dates due to heavy work at office. Can you help me?

ASSISTANT: Sure, please give me a moment to check it.

USER: Ok, take your time.

ASSISTANT: Thank you for waiting, there is no reservation found for the user name when I have checked in our previous booking list.

USER: Its ok, I guess I made a mistake while booking. Anyways, thank you for the information.

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