You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: I am Joseph Williams.

ASSISTANT: How may I serve you today?

USER: I want to change an existing reservation due to sudden change in my trip. Can you help me?

ASSISTANT: Sure, give me a while.

USER: Ok.

ASSISTANT: Thanks for waiting, we did not found any reservation found on this name.

USER: No issue. Thank you.

ASSISTANT: Thanks for opting us.