You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: This is Benjamin Thomas.

ASSISTANT: Yes Benjamin, how can I help you?

USER: I want to change my existing reservation.

ASSISTANT: OK, please wait for a while. I will check and let you know.

USER: OK.

ASSISTANT: Sorry Benjamin, with respect to your name no reservation is there in database.

USER: OK.

ASSISTANT: Thank you for choose us.