You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I assist you at this moment?

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

ASSISTANT: Sure, I will help you in changing, please hold on for a moment to check your reservation status.

USER: Sure.

ASSISTANT: May I know your name please?

USER: My previous reservation has done with the name Mary Allen.

ASSISTANT: Allen, there is no any active reservation with your name in my database.

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

ASSISTANT: It's my pleasure.