|First, you need to ensure you've connected the second router properly.|
Click on my name above in this response and read my “how-to” guide titled, “Add a second Router to your LAN” You will want to use Version 2 where you interconnect the two routers LAN port to LAN port.
If your wireless network (WLAN) is properly configured and working on your existing router, the only thing you should have to do on the second router is duplicate the WLAN settings (ie: SSID name, encryption level and key) on the second router, disable DHCP on it (clients will get DHCP from the original router) and put it on a different wireless channel from the original router's WLAN settings.
So, if for example router 1's WLAN is set to channel 1, put router 2's WLAN on channel 7 or 11
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.