The short answer
Start early and work in short spaced sessions, practise by answering questions from memory rather than re-reading notes, and use past papers under real time limits. Re-reading feels productive and is the weakest way to prepare.
The way most learners revise — reading through notes until they feel familiar — is comfortable, and it is close to the least effective method available. Two changes make more difference than any amount of extra hours.
Retrieve, do not re-read
Close the book and write down everything you can remember, then check what you missed. It feels harder and worse than reading, which is exactly why it works: the effort of pulling something out of memory is what fixes it there. Familiarity is not the same as recall, and only one of them is available in an exam room.
Spread it out
Four half-hour sessions across four days beat one two-hour session, by a wide margin. Cramming produces knowledge that survives until roughly the end of the exam.
Use past papers properly
Not as reading material — sit one, timed, without notes. It teaches pacing, shows how questions are actually worded, and finds the gaps while there is still time to fix them. Then mark it honestly against the memorandum.
Work on what is wrong
Revision drifts towards the comfortable topics. Keep a short list of what came out wrong and work from that list. It is unpleasant and it is where the marks are.
Sleep
The night before matters more than the extra hour of revision it costs. Recall and reasoning both degrade sharply when tired, and those are the two things an exam tests.
For parents
Your job here is mostly logistics and calm: a quiet space, a realistic plan, and not adding pressure to a learner who has plenty already. If anxiety rather than preparation is the problem, say so in the parent forums — it is common, and it is treated differently.