You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I serve you?

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

ASSISTANT: Sure, please be on hold.

USER: Ok, take your own time.

ASSISTANT: Thank you for your time. Sorry, there is no reservation matching with your name in our portal to make changes further.

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

ASSISTANT: Thank you for reaching us.