You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. What can I do for 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, may I know on whose name the previous ticket booking is done?

USER: My previous reservation has done with the name Daniel Brown.

ASSISTANT: Please wait. Ok, there is no reservation found on the name which you have provided.

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

ASSISTANT: Welcome.