The recruiter can help you to learn about ASVAB by providing you with a list of topics and study material. And maybe this is a good material to help you build a real knowledge base. The only way to truly master the exam is to do online ASVAB word knowledge practice test style training questions.
Studying ASVAB related topics is not enough to prepare you for future exams. To truly master the ASVAB format, you will also need to practice exam-style questions. During basic training, the training sergeant or training teacher often uses the term "muscle memory" to describe the training and preparation process.
The idea is that you not only learn everything you need to know about a specific endurance routine, but you should also practice that routine regularly to prepare your muscles and keep them in shape by repeating those exercises.
When you prepare for a physical event such as swimming the 3 miles or more, part of your exercise should mimic the actual event. This is because your body not only needs to be physically fit, it also needs to get used to the sport in question. Your muscles must be properly built to calm down with the activities you do.
This means taking hands-on exams, grading and studying, and becoming familiar with ASVAB-style quizzes and additional practice material.
This will not only expose you to the test style, it will also help your mind develop the ASVAB version of "muscle" memory. After completing a series of live exams, your real ASVAB will be like "just a practice test" and you will feel calmer and more confident overall.