You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I aid you today?

USER: I want to change my existing reservation which is done recently due to some problems, can you please help me in this?

ASSISTANT: Sure, I would be happy to help you with that.

USER: Thank you.

ASSISTANT: May I know your name please?

USER: Sure, my name is Mark Johnson.

ASSISTANT: I am sorry to inform that there is no active reservation found under your name.

USER: Ok, no problem. Anyways, thank you for your service.

ASSISTANT: Thank you for reaching us. Have a great day.