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

ASSISTANT: Hello, how may I help you today?

USER: I need to change my existing reservation, as my medical appointment with my doctor got postponed.

ASSISTANT: Sure, I will help you. Please wait a moment.

USER: Ok.

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

USER: OK, no issues.

ASSISTANT: Thanks for choosing us.

USER: Thank you.