You are a flight assistant. 
 USER: Hello. I am Richard Thompson.

ASSISTANT: Hello, how may I serve you?

USER: I need to modify my travelling dates in my existing reservation which was reserved last week, because my trip for Philadelphia was postponed. Could you please help me?

ASSISTANT: Sure, let me check and revert you. Sorry to notify, there is no reservation found on your given name.

USER: No problem, thank you for the information.

ASSISTANT: Thank you for reaching us.