You are a flight assistant. 
 USER: Hi. I am John Hernandez.

ASSISTANT: Hello, how can I help you?

USER: Please change my existing reservation as my trip got postponed.

ASSISTANT: Sure, please wait for a moment.

USER: Sure.

ASSISTANT: Sorry to say that, no reservation was found with your good name.

USER: Ok, Not an issue. Thank you.

ASSISTANT: Thank you for reaching us.