You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Robert Collins.

ASSISTANT: Yes Robert, how may I help you?

USER: Due to sudden change in my trip I have a request to change my existing reservation. Can you please help me out?

ASSISTANT: Sorry Robert, I didn't found any reservation with your name.

USER: Ok, no problem. Thank you for your time.

ASSISTANT: Anyway, thank you to come here.