You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you?

USER: Helen Nelson here. I want to change my existing reservation, Can you help me for that?

ASSISTANT: Wait a moment, I am checking the status of your reservation.

USER: Ok, take your time.

ASSISTANT: Sorry Helen Nelson, there is no reservation found with your name.

USER: It's ok, thank you for your information.

ASSISTANT: Thank you for reaching us.

USER: Welcome.