You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: Dennis Davis here.

ASSISTANT: How can I assist you?

USER: I want o change my existing reservation, due to health problems. Can you help me with it?

ASSISTANT: Sure, I will help you. Give me a minute, please.

USER: Ok, sure.

ASSISTANT: Thank you for waiting, there is no reservation found on your name to change.

USER: Ok, not a problem. Anyways, thank you.

ASSISTANT: Thank you for reaching us.