You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you?

USER: Catherine Anderson here.

ASSISTANT: Yes Anderson.

USER: I want to change my existing reservation, due to some health issue. Can you please help me?

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

USER: Ok.

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

USER: Not an issue.

ASSISTANT: Ok.

USER: Thank you for checking.

ASSISTANT: Welcome. Thank you for choosing us.