You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you?

USER: Jeffrey Thomas this side, can you help me to change my existing reservation?

ASSISTANT: Sure Thomas, I am here to help to change for your existing reservation.

USER: Sure, take your time.

ASSISTANT: Give me a moment. Sorry Thomas, there is no reservation found in our data base to change your reservation.

USER: Ok, no issues. Thank you for helping me.

ASSISTANT: Welcome. Thank you for choosing us.