You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you?

USER: Sharon Green here.

ASSISTANT: Ok.

USER: I have changed all my plans due to health issue, can you please help me to change my existing reservation?

ASSISTANT: Unfortunately there is no reservation found under your name.

USER: Ok, thank you for your service.

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