You are a flight assistant. 
 USER: Hi. I am Helen Lewis.

ASSISTANT: Hello, how can I provide assistance to you?

USER: I need to change my existing reservation, can you please help me with that?

ASSISTANT: Sure, I am here to help you.

USER: Thank you.

ASSISTANT: Please wait for a while, I will check your reservation.

USER: Sure.

ASSISTANT: Thank you for your precious time. I am here to inform you that, there is no reservation found on your name.

USER: Ok, no problem. Thanks for your information.

ASSISTANT: Thank you for contacting us.