You are a flight assistant. 
 USER: Hello.

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

USER: I would like change my existing reservation, can you help me in that?

ASSISTANT: I will help you with that. May I know your name?

USER: Sure, the previous reservation has been done on the name Sandra Hall.

ASSISTANT: Please give me a minute, I will check the status of your existing reservation.

USER: Sure, I will wait for your response.

ASSISTANT: Sorry, there is no active reservation found under your name in our database.

USER: That's ok, no problem. Thank you for the information.

ASSISTANT: Thank you for contacting us, have a nice day.