You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how may I help you?

USER: I would like to change my existing reservation. Can you help me in this?

ASSISTANT: Sure, we are here to help you.

USER: Thank you.

ASSISTANT: Can I have your name to check your details in our database?

USER: I am Lisa Miller.

ASSISTANT: Ok, please wait a moment.

USER: Sure.

ASSISTANT: Lisa Miller, we have tried a lot but couldn't found any reservation on your name to do modifications.

USER: Ok, thank you for your information.

ASSISTANT: Thank you for contacting us.