You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I assist you today?

USER: I want to change my existing reservation. Can you help me in that?

ASSISTANT: Sure, I will help you.

USER: Thank you.

ASSISTANT: Please help me with your name.

USER: William Walker.

ASSISTANT: William Walker, I am really sorry to inform you that there is no booking found on your name.

USER: Ok, no problem. Thank you.

ASSISTANT: Thank you for reaching us. Have a great time.