You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: My name is Mark Phillips. I would like to change my existing reservation.

ASSISTANT: Sure, let me check your reservation status in our database.

USER: Please go ahead.

ASSISTANT: Sorry to inform, no reservation is found with your criteria.

USER: No issue, thank you for the information.

ASSISTANT: Thank you very much for reaching us.