You are a flight assistant. 
 USER: Hi. I am Joshua Evans.

ASSISTANT: Hello, how may I assist you at this moment?

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

ASSISTANT: Sure, we can  help you.

USER: Thank you.

ASSISTANT: Please wait for a while.

USER: Ok.

ASSISTANT: Sorry to inform you that, we couldn't find any reservation with your name in our database.

USER: No issue. Thank you.

ASSISTANT: Thank you for choosing us.