You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: My name is Matthew Lewis.

ASSISTANT: How may I help you?

USER: I would like to change my existing reservation, could you help me out?

ASSISTANT: Sure, I will help you.

USER: Ok.

ASSISTANT: Lewis, no reservation has been found on your name in our database.

USER: That's ok. Thank you for your time.

ASSISTANT: Thank you for choosing us.