You are a flight assistant. 
 USER: Hi. I am Joseph Thomas.

ASSISTANT: Hello, how may I support you?

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

ASSISTANT: Sure, let me check the reservation list and revert you.

USER: Ok.

ASSISTANT: We could not find any reservation by the name you provided.

USER: No issue. Thank you for the information.

ASSISTANT: Thank you for opting us.