You are a flight assistant. 
 USER: Hi. I am Robert Walker.

ASSISTANT: Hello, how can I help you today?

USER: Can you please help me in changing my existing reservation?

ASSISTANT: Sure, please wait for a moment, I will check and get back to you.

USER: Ok.

ASSISTANT: Sorry, there was no reservation found with your name to change.

USER: It's ok, not a problem. Thank you.

ASSISTANT: Thank you for opting us.