You can complete the Https://fritz.repeater setup by creating an secure connection via WPS between your router and Extender Just place your extender is same room where your router is placed for better network connectivity
Plugged in the extender switch on electric outlet and switched it "ON" it will start with blinking LED Light
Now, press the WPS button of your old router which is available on the back side of your router for 2 second's and release it
Do same with your extender press WPS button of your extender (You have to press within 2 minutes of pressing the button of router)
After some time your Extender will establish the connection via WPS with your router
Now, Ready to use
So In this way you can easily setup your Fritz.repeater.