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

ASSISTANT: Hello, how may I assist you?

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

ASSISTANT: Sure, hold on for a moment. Let me check.

USER: Ok, take your time.

ASSISTANT: Sorry David, there are no flights reserved on your given name.

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

ASSISTANT: Welcome, thank you for choosing us. Have a great day.

USER: Welcome.