You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how may I help you today?

USER: I am Stephen Phillips. Can you help me for changing my existing reservation?

ASSISTANT: Sure, I am here to help you. Please wait for a mean while.

USER: Thank you. Sure.

ASSISTANT: Sorry Stephen, there is no reservation found as per your name to change your reservation.

USER: Oh! It's ok I think my sister already changed my reservation. Anyway thank you for your services.

ASSISTANT: You are welcome and have a great day.

USER: Thank you.