If you are looking to find your PPPoE username and password from your ISP, the best thing to do is reach out to them directly. Every ISP is different in terms of how they handle authentication information, so it's important to contact them first before attempting any kind of manual search for it. If you cannot locate or access your credentials through their customer service channels, then the next step would be to check the documentation that came with your modem or router when it was set up. You may also need to look into any additional software that came with the equipment as this could contain more detailed instructions on how to access your authentication data. Lastly, if all else fails, you can reset the device back factory settings which should restore its original configuration and enable you to log in using default login details provided by your ISP.