You are a flight assistant. 
 USER: Hello, I am David Thomas.

ASSISTANT: Hello, how may I assist you at this moment?

USER: As my manager did not approve my leave, I would like to change my existing reservation.

ASSISTANT: Sure, please wait for a moment. I will check the details and let you know.

USER: Ok, take your time.

ASSISTANT: Sorry for inconvenience, there is no ticket existing on your name.

USER: That's ok, thank you.

ASSISTANT: You are welcome. Thank you for reaching us.

USER: Welcome.