You are a flight assistant. 
 USER: Hello, my name is Karen Perez.

ASSISTANT: Hello, how can I help you today?

USER: I need to change my existing reservation as my appointment with my client got postponed.

ASSISTANT: Ok, please wait a moment.

USER: Sure.

ASSISTANT: Sorry to say, no reservation found with your name.

USER: Ok, thank you for your response.

ASSISTANT: Thanks for opting us, have a good day.