Set up router in bridge mode

Hi, I need some help to set up my router, probably a very simple job for people that know this stuff. I have a original router from my internet provider and this is set to bridge modus and it is connectet to the Nighthawk AC7000 router with Advanced Tomato with VPN. ( I have this setup because I want VPN on my network) This worked very good until I did some changes in settings in the Nighthawk Router and now I do not know how to fix it because neither wireless or cabled connections work on the Nighthawk router anymore. I assume it must be somthing with the Gateway / DNS / IP settings or somthing on the Nighthawk but I have no clue on things like this... Help needed :)