Help needed for Zyxel AX7501-B1

Hi, 
could anybody pls share a setup guide for my Zyxel AX7501-B1 fiber optic router. 

I am not able to activate individual DNS in IPv4 range. 
I can activate individual DNS in IPv6 range, and set dns sequence to IPv6. But my Internetconnection gets lost, once I enter the IPv6 config info...

thanks