You are a flight assistant. 
 USER: Hi,.

ASSISTANT: Hello, how may I assist you today?

USER: I want to change my existing reservation due my joining date has been postponed. Can you aid me with this?

ASSISTANT: Sure, we are glad to serve you.

USER: Thank you.

ASSISTANT: Please share your name to proceed further?

USER: I am Sandra Nelson.

ASSISTANT: Ok, please wait a minute, let me check your reservation and revert to you.

USER: Ok.

ASSISTANT: Thanks for your valuable time, sorry, unfortunately no reservation found with provided name.

USER: Not really a problem. Thank you for your prompt response.

ASSISTANT: Thank your for picking us, have a pleasant day.