You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I assist you?

USER: I want to change my existing reservation, can you please help me?

ASSISTANT: Yes, can you share me your name?

USER: I am Mary Clark.

ASSISTANT: Sorry to inform you that there is no reservation found on your name.

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

ASSISTANT: Thank you for reaching us.