You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I aid you?

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

ASSISTANT: Sure, I am here to help you out. Please allow me a moment.

USER: Sure, I will wait for your response.

ASSISTANT: Thank you for waiting. Here, there is no active reservation have been found under your name in our database to change it.

USER: That's ok, thank you for checking.

ASSISTANT: Thank you for reaching us.