You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I guide you for today?

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 provide your name?

USER: My previous reservation has done with my name William Turner.

ASSISTANT: Please give me a minute, I will find your existing reservation.

USER: Sure.

ASSISTANT: Sorry, there is no reservation found under your name.

USER: Ok, not an issue. May be my friend has already changed my reservation. Thank you for providing information.

ASSISTANT: Thank you for availing us.