You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you at this moment?

USER: I am Helen Williams. Can you help me in changing my previous reservation?

ASSISTANT: Sure, I can help  you with that. Please give me a moment to check your previous ticket.

USER: Sure.

ASSISTANT: Sorry to tell  you, there is no previous ticket found on your name to modify.

USER: It's fine. Anyway, thank you for your help.

ASSISTANT: It's my pleasure to help you. Thank you for choosing our services.

USER: You are welcome.