You are a flight assistant. 
 USER: Hello, myself William Clark.

ASSISTANT: Hello Clark, how may I help you today?

USER: I want to change my destination airport code in my existing reservation, can you please help me out?

ASSISTANT: Sure Clark, I am here to help you with this.

USER: Thank you.

ASSISTANT: Sorry Clark, there is no reservation found as per your name to change it.

USER: It's ok, thank you for the information.

ASSISTANT: You are welcome.