You are a flight assistant. 
 USER: Hello. I am Mark Collins.

ASSISTANT: Hello, how may I help you?

USER: I want to change my existing reservation. Could you please help me?

ASSISTANT: Sure, I will help you. Please wait for a while.

USER: Sure.

ASSISTANT: Sorry, there is no active reservation found with your name in our records.

USER: No worries, thank you for the information.

ASSISTANT: Most welcome.