You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I serve you?

USER: I need change my existing reservation. Can you please help me out?

ASSISTANT: Sure, to change your reservation I need to know your name?

USER: Alexander Mitchell.

ASSISTANT: Sorry to say that, no reservation found with your name to change the reservation.

USER: OK. Thank you.

ASSISTANT: Thanks for choosing us, have a nice day.