You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: I am Helen Williams.

ASSISTANT: How may I help you?

USER: Can you help me for changing my existing reservation?

ASSISTANT: Sure, I will help you. Please wait a minute.

USER: Thank you. Ok.

ASSISTANT: Sorry to tell you, there is no reservation found on your name.

USER: Oh! It's ok, no problem. Thank you for your services.

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