You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: Can you please help me in changing my existing reservation?

ASSISTANT: Sure, I am here to help you for this. May I know your name please?

USER: I am Donald Clark.

ASSISTANT: Please wait for a while, let me check your reservation status in our database.

USER: Ok.

ASSISTANT: Sorry for inconvenience, no reservation is found with your criteria.

USER: Ok, no problem. Thank you.

ASSISTANT: Thank you very much for contacting our agency.