You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you today?

USER: I am Mark Brown. Due to my health problem I want to change my reservation, can you please help me to change my reservation?

ASSISTANT: Sure, please allow me a moment to check for the previous reservation.

USER: Sure, I will wait.

ASSISTANT: Mark, there is no reservation found under your name.

USER: That's fine. Thank you for  your service.

ASSISTANT: Thank you for reaching us.