You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I help you?

USER: I want to change my reservation due to health problem, can you help me?

ASSISTANT: May I know your name please?

USER: Myself Sandra Mitchell.

ASSISTANT: Sorry, there is no reservation matching with your name in our portal to make changes further.

USER: No problem, thanks for checking.

ASSISTANT: Most welcome.