connecting a second wired router ASUS RT-AC68R

I use your gateway router/modem.   I have a dead spot at one end of the house, and I have a Cat 5 cable from the gateway to a closet near the dead spot.    I have tested the cable on a PC and it is good.   I own an ASUS RT-AC68R and have googled how to set up a second router.   I have logged into your gateway at 10.0.0.1, but I am hesitant to make changes.   Do you have an article explaining what gateway setting changes I should make?   I basically just want the ASUS to serve as a wired repeater.   I know you sell xFi pods, but I would prefer not to spend $125 when I own the ASUS and have a cable.   Thank you