You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you today?

USER: Actually my sister's engagement got postponed so that I want to change an existing reservation, can you help me?

ASSISTANT: Sure, I will help you that.

USER: Ok, sure.

ASSISTANT: Please give me a minute, I will come back with your details. May I know your travelling dates?

USER: Sure, I am Rebecca Williams. And I want to travel on 07/28 to 07/30.

ASSISTANT: I need your airport codes to proceed the booking?

USER: My changed airport codes are DFW from LAS.

ASSISTANT: Wait for a moment, I will check  it.

USER: Make sure that the connection limit is 1. Ok.

ASSISTANT: I did not find any flight with your details.

USER: Ok, no problem. Thank you for your information.

ASSISTANT: Thank you for your reaching us.