Hello   @Dek1502 

If modem router or router Wifi network is gone, double check if you accidentally turned off Wi-Fi function by pressing Wi-Fi button. 

If that does not help, call the router support or internet provider to get the main router Wifi network back first. 

Then pair powerline devices, and connect main power adapter to router, and put power line extender in the place where you wish to extend the Wifi network. Here is a guide of changing wifi settings for Wi-Fi powerline unit. 

How to customize wireless settings on tpPLC Utility (new logo)?