You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you?

USER: My name is Charles Garcia. I need your help to book a flight ticket.

ASSISTANT: OK Charles.

USER: Actually I want to change my existing reservation. Can you please help me with that.

ASSISTANT: OK, please wait so that I can check the details.

USER: Sure.

ASSISTANT: Yes, I can help you.

USER: Thank you.

ASSISTANT: Sorry, I did not find any existing reservation on your name.

USER: OK. Thank you for the information.

ASSISTANT: Thank you for reaching us.