You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you?

USER: I am David Williams. I want to change an existing reservation, due to my family tour trip got postponed.

ASSISTANT: Ok, please wait for a moment.

USER: Sure.

ASSISTANT: Sorry, no reservation found with your name.

USER: Not an issue. Thank you.

ASSISTANT: Thank you for opting us.