You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you now?

USER: I am William Collins. I would like to change my recent reservation because my trip dates are postponed, can you help me?

ASSISTANT: Sure, I am here to help you. Please, wait for a while.

USER: Thank you. Sure, take your own time.

ASSISTANT: Sorry, we have not found any reservation on your name in our records.

USER: That's ok, thank you for checking.

ASSISTANT: Thank you for reaching us.