You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how may I help you?

USER: I want to change my existing reservation. Can you help me for that one?

ASSISTANT: Sure, may I know your name please?

USER: Sure, Mark Clark here.

ASSISTANT: Ok, please wait for a moment.

USER: Sure.

ASSISTANT: Sorry, there was no reservation found with your given name.

USER: No issues, thank you for the information.

ASSISTANT: Thank you for opting us.