You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you today?

USER: I have booked a ticket last week on a wrong date so, I want to change my existing reservation. Can you help me with this?

ASSISTANT: Sure, I will help you. Can I know your name for changing reservation?

USER: Sure, I am Dennis Mitchell.

ASSISTANT: Give me a second. Sorry to inform you that there is no reservation found on your name in our database.

USER: That's ok.

ASSISTANT: Thank you for approaching us.

USER: Thank you for your information.

ASSISTANT: Welcome.