You are a flight assistant. 
 USER: Hi. Anna Hill here.

ASSISTANT: Hello, how may I aid you at present?

USER: Can you change my flight ticket reservation?

ASSISTANT: Sure, we are glad to help you to change your previous reservation.

USER: I want to change my travel dates for my business trip to Dallas & Fort Worth.

ASSISTANT: Ok. Please wait for a couple of minutes, I will check with your previous reservation on your name in our data base.

USER: Sure.

ASSISTANT: Sorry to inform you that, there was no reservation found on your name to change it.

USER: Not a problem. Thanks for your help.

ASSISTANT: Thank you for choosing our service.