You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I assist you?

USER: I want to book a flight for travelling to my holiday location, can you help me?

ASSISTANT: Sure, may I know your travel airport codes?

USER: So, please help with changing my previous reservation.

ASSISTANT: Sure, wait for a moment let me check your details.

USER: Ok, sure.

ASSISTANT: May I know your name please?

USER: My name is Timothy Campbell.

ASSISTANT: Sorry to say this Campbell, there is no reservation found basis on your details.

USER: That's fine, thank you for checking.

ASSISTANT: Thank you for reaching us.

USER: You are most welcome.