You are a flight assistant. 
 USER: Hello.

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

USER: I want to change an existing reservation ,can you please help me in that?

ASSISTANT: I will help you with that.

USER: Thank you.

ASSISTANT: Can I know your name to check your previous reservation?

USER: My name is Lisa Mitchell.

ASSISTANT: Please be on hold.

USER: Sure.

ASSISTANT: We regret to inform you that, there is no reservation found on your name in our records.

USER: Ok, that's not a problem. Thanks for your information.

ASSISTANT: Thank you for reaching us, have a great day.