First, place the power plug of the Linksys RE6400 WiFi range extender device in the power socket. After that, stand by to see the solid power LED start flashing on a Linksys device. Next, press the WPS button of your Linksys RE6400 WiFi range extender. Later, push the WPS button on your house's main router. Now, the WPS LED starts flashing solid blue on both extender and router gadgets. Thus, the solid LED defines that the extender and router are successfully linked with each other. 

Now, the Linksys re6400 setup  process is done. If you are facing trouble after doing the setup process then try placing the extender closer to the router.