Thanks for the suggestions I found the solution for anyone who finds this.
iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE
iptables -t nat -I PREROUTING -i br0 -p tcp --dport 53 -j DNAT --to 192.168.1.2:53
iptables -t nat -I PREROUTING -i br0 -p udp --dport 53 -j DNAT --to 192.168.1.2:53
iptables -t nat -I PREROUTING -i br0 -p tcp -s 192.168.1.2 --dport 53 -j ACCEPT
iptables -t nat -I PREROUTING -i br0 -p udp -s 192.168.1.2 --dport 53 -j ACCEPT
I ran these commands directly on the Asus RT-AC68R router via SSH using putty. This will force any DNS client change to use pihole. it will take a few minutes for it take effect. also credit for the commands go to Lethal