Okay ladies I need help and help fast!!!

So my SO has worked over two years at his job (oilfield) and his boss hasn't given him the raises or promotion like he should've. The boss has actually brought in his EX SON IN LAW which he's already gotten them fat asf raises and even a fckn promotion!! He hasn't been there even a year..and the boss won't listen to my SO and his concerns. Well today, the shop hand in another state sent my fiance papers to certify tool which he's not certified to. The boss pretty much said "oh well".. Now my fiances frantic about doing that just in case something goes wrong with it and another shop sues them, he doesn't want his name in the problem because he's stated clearly he's not certified to do so. So now it's pretty much a game of I do this or I quit kinda thing. I hope this made sense. I told him to leave a letter where boss will find it, that states the concerns about EVERHTHING (every problem listed in this) but he says he doesn't want to talk to him until he quits. 🤐🤐🤐 I need help telling him it's not in his best bet to quit and just to write to him. Or hell even call him. But he don't listen to me. Smdh