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

ASSISTANT: Hello. How can I assist you?

USER: I want to reschedule my existing reservation, due to some emergency. Can you help me to do some modifications?

ASSISTANT: Sure, I will help you to change your reservation. Give me a moment.

USER: Take your time.

ASSISTANT: Sorry, there is no reservation found on your name to change.

USER: No issues. Thank you for checking.

ASSISTANT: Welcome. Thank you for choosing us.

USER: You are welcome.