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

ASSISTANT: Hello, how may I be at your assistance?

USER: Can you please help me in changing my existing reservation?

ASSISTANT: Sure, please standby.

USER: Ok.

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

USER: Ok, no problem. Thank you for your help.

ASSISTANT: Thank you for reaching us.