Need Help with Pi-Hole Setup

Hi. I installed Pi-Hole on a Raspberry Pi 3 and it's IP my network is 192.168.xx.xxx.

I want to set up my Asus RT-AC86U. In my router setup, where do I put in the IP address:

(1) Advanced Settings > LAN > DHCP Server > DNS Server

or

(2) Advanced Setting > WAN > WAN DNS Setting > DNS Server 1

Thanks in advance.