If you are re-certifying through the same agency, then perhaps the study guide would be fine. If you are certifying through a new agency, then I would not just rely on an online manual. Each agency and the exam are different and the exams will not be the same. (I’m a little confused by your statement of “after a period of 5 years online”. Can you clarify?).
I would contact the certifying agency and talk to a representative so they can guide you on the best way to study and what prerequisites are needed.