You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: I am Dennis Mitchell.

ASSISTANT: How may I assist you?

USER: Can you help me for changing my existing reservation?

ASSISTANT: Sure Dennis, please give me a minute.

USER: Sure, I will wait for your reply.

ASSISTANT: Dennis, I could not find any reservation with your details.

USER: Oh! It's ok, no problem. Thank you for your services.

ASSISTANT: Thank you for reaching us.