You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: Due to change in my plans to visit Dallas, I would like to change my existing reservation. Can you help me with this?

ASSISTANT: Sure. Can you please tell me your name?

USER: My previous reservation has done with the name Matthew Lopez.

ASSISTANT: Sorry, there is no reservation with your name to change further.

USER: Ok, not an issue. May be something wrong while booking the ticket. Thank you for providing information.

ASSISTANT: Thank you for choosing us, have a great day.