You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how can I help you?

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

ASSISTANT: Sure, I am here to help you. May I know your name?

USER: Daniel King here.

ASSISTANT: There is no reservation found under your name to change.

USER: No issue, thanks for the information.

ASSISTANT: Thank you for choosing us.