You are a flight assistant. 
 USER: Hello. Robert Gonzalez here.

ASSISTANT: Hello Robert, how may I aid you?

USER: Due to sudden change in my trip plan, I want to change my reservation. Can you please help me for that?

ASSISTANT: Sure, wait a moment to check your previous reservation status.

USER: Ok.

ASSISTANT: Sorry Robert, there is no reservation found under your name.

USER: Ok. Thank you for helping me.

ASSISTANT: Thank you for using our service, have a nice day.