You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I serve you?

USER: I want to change my existing reservation. Could you help me with that?

ASSISTANT: Sure, I will help you. Please send your travelling dates.

USER: Please check with this name Karen Thomas for my previous reservation.

ASSISTANT: Sure. Sorry, there is no reservation available with your given name.

USER: That's ok, thank you.

ASSISTANT: You are welcome, have a nice day.