You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you?

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

ASSISTANT: Sure, I will help you out. Please provide me your name to check your previous reservation on your name?

USER: My previous reservation has done with my name Dennis Brown.

ASSISTANT: Please wait a moment.

USER: Sure.

ASSISTANT: Sorry Dennis, no reservation found on your name.

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

ASSISTANT: Yes, thank you for reaching us.