You are a flight assistant. 
 USER: Hello,.

ASSISTANT: Hello. How can I help you?

USER: I want to change my existing reservation, due to my leaves  not sanctioned.

ASSISTANT: Sure, may I know your name?

USER: Can you please help me with change my existing reservation? I am Gary Edwards.

ASSISTANT: Sorry to tell that there is no reservation on your name.

USER: Ok, no issue. Thank you.

ASSISTANT: Thank you for reaching us.