You are a flight assistant. 
 USER: Hi. I am Dennis Johnson.

ASSISTANT: Hello, how may I assist you today?

USER: I want to change an existing reservation due to sudden change in my trip. Can you help me with this?

ASSISTANT: Sure, we are here to help you. Please wait a moment.

USER: Ok.

ASSISTANT: Thank you for your time, unfortunately no reservation found on your name.

USER: No issue. Thank you.

ASSISTANT: Thank you for availing us.