investigate breech of pos retail software and customer list

I am in need of assistance as I have recently experienced a breach in my retail POS software. Customers have yet to be notified of the breach, so I need help in investigating the source of it. Specifically, I need someone to analyze the source of the breach and identify the root cause. If you have the expertise and are available to tackle this problem, I would be most thankful for your help. The business is a spa that utilizes amazon alexa for background noise. Without my knowledge my partner transferred the alexa to her account and recorded and redistributed every customer interaction I have had.