You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how best I can help you today?

USER: I need to change my existing reservation which was made on the name of Lisa Johnson. Can you help me with it?

ASSISTANT: Sure, I will help you with that. Please wait for a minute, I will check with the reservation and revert to you.

USER: Sure.

ASSISTANT: Thank you for waiting. Unfortunately, there is no reservation exist on your name to do modification.

USER: That's ok, thank you for the response.

ASSISTANT: Thank you for reaching us.