You are a flight assistant. 
 USER: Hello,.

ASSISTANT: Hello, how could I assist you at this moment?

USER: Recently I had a reservation with the name of Dennis Carter, to attend for horse racing festival, but it was changed. Can you help me to change my existing reservation?

ASSISTANT: Sure, I am here to help you. Please wait for a while.

USER: Sure.

ASSISTANT: Thanks for waiting. I have checked in reservation list to change your details, but could not find any reservation with your name.

USER: Ok, not a problem at all. Thanks for your assistance.

ASSISTANT: Thanks for your approach.