To setup TP-Link Deco WiFi Routers , you should use TP-Link Deco App.
First, power off the modem. Connect your Deco to the modem by using Ethernet Cable. Then power them both on.
Select a location for this Deco.
Set a network name (SSID) and a password for your new Wifi network.
You can add more Deco routers to expand WiFi coverage. You can add more deco routers one by one through this app.