You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I aid you today?

USER: I am Mark Harris. I want to change my existing reservation due to health issues, can you please help me with that?

ASSISTANT: Sure, please wait.

USER: Ok.

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

USER: Not an issue, thank you.

ASSISTANT: Thank you for reaching us.