You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist 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, could you please provide your name to check your reservation status?

USER: My previous reservation has done with my name James Williams.

ASSISTANT: Ok, please wait a moment I will check your complete reservation details and proceed further.

USER: Sure, take your own time.

ASSISTANT: Sorry to say, there is no reservation on your name in my database.

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

ASSISTANT: Than you for choosing us, have a nice day.