You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you?

USER: I want to change my existing reservation. Can you please help me with this?

ASSISTANT: Sure, can you please provide me your name to check the reservation?

USER: I am Melissa Green.

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

USER: Ok, not an issue.

ASSISTANT: Thank you for reaching us.

USER: Thank you for checking.