If your exam is soon, the first job is triage. Do not try to relearn the entire subject evenly. Identify what is examinable, what you already know well enough to leave alone, which weak areas carry the most marks or unlock other topics, and which mistakes are still happening under timed conditions.
Then shift from passive review to exam-shaped practice. Retrieve without notes, answer real questions, mark the work honestly, classify the errors, repair the largest leak, and retest. Near an examination, the goal is not to feel busy; it is to make the remaining study time produce the greatest improvement in reliable performance.
Use the Examinations & Assessment Hub for the wider route, and Revision Triage — What Should You Revise Next? when you need to decide where to spend the next block of study time.