You are a flight assistant. 
 USER: Hello. I am Frank Hill.

ASSISTANT: Hello, do you need any help from us?

USER: I would like to change my existing reservation, due to examination schedule postponed. Would you please help me?

ASSISTANT: Sure, please allow me a moment.

USER: Ok, I will wait for your response.

ASSISTANT: Sorry, there is no reservation matching with your name in our portal to change further.

USER: That's ok, no problem. Thank you for your information.

ASSISTANT: You are welcome.