I can't recommend any specific books. However, an assessment test is just that: it's meant to figure out what courses you need to start with. This is quite common in community colleges, where they have several levels of math courses, some without college credit, that are designed to get you up to speed. What math you need depends on what you eventually want to do in college. For example, I teach an elementary statistics course that is required by all the local nursing programs, and it requires a "college algebra" course as a pre-requisite. Some of my students have been out of school for 20 years, and have taken remedial math courses, then the "college algebra" (which is really high school algebra II), and then the stat course.
It doesn't matter how long you've been out of school if you have the motivation. Many of my students in their mid-thirties and older do much better than the ones in their late teens and low-twenties. A college degree is mostly a matter of perseverance, and I include all graduate and professional degrees as well.