You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how can I help you?

USER: Please help me to change an exiting reservation as I need to change my trip dates.

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

USER: I am Mary Nelson.

ASSISTANT: There is no reservation found under your name.

USER: That's ok, no issue. Thank you.

ASSISTANT: Thank you for choosing us.