You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you today?

USER: I am David Williams want to change my reservation due to prepone of my office Annual Bash. Can you help me in changing my reservation?

ASSISTANT: Sure, please wait for a moment, I will check and get back to you.

USER: Sure.

ASSISTANT: Sorry, there was no reservation found with your name.

USER: Ok, no issues. Thank you for your response.

ASSISTANT: Thank you for choosing us.