Plug your TP-Link Range Extender into a power outlet near your TP-Link router. Push the WPS button on your main router first, then immediately push the WPS button on your range extender.
After you have pushed WPS button of your router, you need to push WPS button of your range extender within 2 minutes. After this, log into the router's web-based management page and configure WAN Connection Type.
Enter your PPPoE username and password which are provided by your ISP. Click on Save button to save your settings, then the router will connect to the internet after a while.
How Can I Connect TP-Link Range Extender to TP-Link Router?