You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: I am Robert Harris. Actually, there is small change in my journey. Can you help me to change my existing reservation?

ASSISTANT: Ok. Wait a minute, I will check once your previous reservation.

USER: Ok.

ASSISTANT: Sorry Robert, there is no reservation.

USER: It's ok. Thank you for your service.

ASSISTANT: Most welcome.