You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: John Clark here.

ASSISTANT: How can I assist you, John?

USER: I would like to change my reservation due to health issue, can you help me?

ASSISTANT: Sure John, please give me a minute.

USER: Ok, I will wait for your reply.

ASSISTANT: John, there is no reservation found with your details.

USER: It's ok, no problem. Thank you for checking.

ASSISTANT: Thank you for reaching us.