Pihole Help

Hi everyone, 

I need some help with my Pihole set up and the guide that Firewalla has posted. I followed their guide here and couldn't get the DNS to get set up on my main network. 

https://help.firewalla.com/hc/en-us/articles/360062551673-How-to-run-external-pi-hole-on-the-Firewalla

Additionally with the two networks set up I am unsure how to get into the PiHole GUI from my main network. Do I need to bridge the networks somehow? 

Any help would be greatly appreciated since my fiance demands more ad blocking on our network. 

Thank you very much in advance!