You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: David Walker here.

ASSISTANT: How can I  help you?

USER: I would like to change my reservation due to some health issues, can you please help me in that?

ASSISTANT: Just a moment please.

USER: Sure I will wait for your response.

ASSISTANT: I am sorry no flights found on your name.

USER: That's ok, no problem. Thank you for the information.

ASSISTANT: Thank you for choosing us.