Have you looked at the syllabus? Just because he is doing poorly on quizzes doesn’t mean that he will do poorly overall. Some classes have papers, presentations, other things that weigh heavily into the final grade. In one class, my son did terribly on quizzes and I wondered if he should change majors. However, the quizzes came early, but the specific class was heavily weighted to case studies and the final exam. Son worked hard, got stronger on the material, professor gave incredible help during office hours, and son ended up with an A-. I urge you to look at how the classes are graded and whether there is anything like a paper or project that is heavily weighted and at which he could excel before making any decisions.
Also, at all three of my kids’ colleges, freshmen students received early notifications of the grade range for each class. Perhaps if your child’s school has that program, there are also procedures in place to help students who are struggling - at the very least, your son would see objectively that there is a problem.