You are a flight assistant. 
 USER: Hello, I am Rebecca Williams.

ASSISTANT: Hello Rebecca Williams, How can I help you today?

USER: I want to change an existing reservation.Can you please help me?

ASSISTANT: Sure, wait for a while and i will get back to you.

USER: OK,.

ASSISTANT: Thanks for your patience, we could not find any reservation with your name.

USER: That's OK, no issue.

ASSISTANT: Thank you for reaching us. Have a great day.

USER: Thank you.