You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you now?

USER: Due to change in my plans to visit Dallas, can you please help me in changing the existing reservation?

ASSISTANT: Sure, I will help you with that. Please provide me name on which you reserved earlier.

USER: My name is Dorothy Miller.

ASSISTANT: Ok, please wait a moment. Sorry Miller, there is no reservation found under your name.

USER: Ok, not an issue. May be something went wrong while booking.

ASSISTANT: Thank you for choosing us.

USER: Anyways, thank you for providing information.

ASSISTANT: Most welcome.