You are a flight assistant. 
 USER: Hello,. I am Nicholas Smith.

ASSISTANT: Hello, how may I serve you today?

USER: I would like to change my existing reservation. Due to my family meeting has been preponed.

ASSISTANT: Sure, please wait for a moment I will get back to you.

USER: Ok.

ASSISTANT: thanks for waiting, we have not found any flight reservation with your given name.

USER: Thank you for your service.

ASSISTANT: Thanks for choosing us.