You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you?

USER: Due to my ill health, I couldn't make my trip to Dallas. I would like to change my existing reservation. Will you help help me with this?

ASSISTANT: Sure, may I know your name?

USER: My name is William Williams.

ASSISTANT: Please wait for a moment.

USER: Sure.

ASSISTANT: Sorry, no reservation found by your name.

USER: Ok, not an issue. May be something went wrong while booking the ticket.

ASSISTANT: Thank you for contacting us.

USER: Thank you for providing information.