You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: Melissa Anderson here.

ASSISTANT: How may I help you?

USER: I need to change my existing reservation. Can you please help me?

ASSISTANT: Sure, please hold on.

USER: Ok, take your time.

ASSISTANT: Sorry, there is no reservation found on given name.

USER: Ok, no problem. Thank you for checking out.

ASSISTANT: Thank you for reaching us.