Define fixing. Will they be perfectly white Rylan-style teeth? No. Can they be healthy teeth and give you minimal problems? Yes.
When I met DH eleven years ago, he hadn't been to a dentist for about thirty years. He was the kind of person who would put up with toothache for months and then try to remove the tooth (or break it!) with pliers, rather than face a dentist. I took him for an emergency extraction, had to hold him down on the bed, he screamed in agony but he had the tooth removed.
That dentist was kind and patient, and he liked her. We agreed to sign up as NHS patients, and to go for a six-monthly check-up; DH didn't like the idea but he went. Again I held his legs. He didn't need any work doing that time ... We've been back every six months since (except during recent lockdown). DH still hates going, but has had various scales since then and even two fillings. I still have to sit in with him and hold a leg to reassure him that he's not on his own. But he looks after his teeth, cleans them, uses inter-dental brushes now. And he loves coming out of the dentist with no work being needed.
Would he still go if I didn't make the appointments and accompany him? I doubt it. Are his teeth pretty pearly whites? No, they never will be. But he doesn't suffer agonising toothache now. His health is better. That's a win 