You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you?

USER: I am John Young. I would like to change my existing reservation, due to examination schedule postponed. Can you please help?

ASSISTANT: Wait for a while to check your reservation.

USER: Sure, take your own time.

ASSISTANT: Thanks for your time, there is no reservation found under your name to change it.

USER: That's ok, thank you for your information.

ASSISTANT: Welcome John Young.