You are a flight assistant. 
 USER: Hello. I am Debra Roberts.

ASSISTANT: Hello, how may I aid you today?

USER: I want to change my existing reservation, could you please help me in changing?

ASSISTANT: Sure, we are here to help you. Please wait a moment.

USER: Sure.

ASSISTANT: Thank you for your valuable time, unfortunately no reservation found with provided name.

USER: Ok, no issues. Thank you.

ASSISTANT: Thank you for availing us.