You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I assist you?

USER: I want to change my existing reservation which is done recently due to some problems, can you please help me?

ASSISTANT: Yes, I can help you. Can you share me your name for checking?

USER: Thank you. Sure, my name is Brenda Allen.

ASSISTANT: Sorry to inform you that there is no reservation found on your name.

USER: Ok, that's fine. Thank you for your service.

ASSISTANT: Thank you for contacting us.