The Linksys ac1200 device can be installed as an Access Point mode which provides better signal transmission with optimized performance. Although you can do this Linksys ac1200 setup from the web interface there will be a need to make a wired connection. So, connect the existing router to the Linksys ac1200 and connect your device to the extender network. Meanwhile, check if the ethernet LED turns green which denotes the connection is successful. Select the wireless network from your device’s list which is Linksys AP setup-xxx, where xxx is the MAC address. Then, access the setup window on your networked device using the web/IP address. 

The web address of Linksys is extender.linksys.com and the IP address is 192.168.1.1. Make sure you enter any of those addresses without making any mistakes. Afterward, create an admin password and select the password hint if you want to remember it in the future. Then, from the next page select the Access Point option (As a wired range extender) and click on the save button. Now, create your Access Point extended network SSID name and password then click next to complete the process.