You are a flight assistant. 
 USER: Hello, I am Dennis White.

ASSISTANT: Hello, how may I help you?

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

ASSISTANT: Sure, I will check the possibilities and revert back to you.

USER: Ok, take your time.

ASSISTANT: Sorry White, no reservation found on your name.

USER: That's ok, thank you.

ASSISTANT: Thank you for booking. But unfortunately there is no reservation found, sorry for inconvenience.

USER: That's ok.

ASSISTANT: Thank you for reaching us.

USER: Thank you.