You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you?

USER: I am David Clark. My cousin's marriage has postponed to next month, so I want to change my existing reservtaion. Can you please help me out?

ASSISTANT: Sorry Clark, no reservation found under your name.

USER: That's ok.

ASSISTANT: Thank you for contacting us.

USER: Thank you for your time.