If you are confident enough in your English, the demon Kalotes from the book Lucifer and the Hidden Demons can help you learn fast and easily. I’ve summoned this power multiple times and have had good results every time. You still have to study but the demon will assist. There are also demons in the book that can make you calm and clear minded during intense situations, like a high-pressure exam, and other powers that can help with academics.
If you’d rather work with the Goetia demons instead of Lucifer, Demons of Magick and The Magick of Angels and Demons are good books. Back in the day I worked with Barbatos on a science project with good results.
You don’t need to have dramatic manifestations in the ritual for the magick to work. Follow the instructions and the demon will hear you, whether you sense the demon or not.
For some mundane advice, focus on testing yourself, not rote repetition. Think of it this way. On the actual exam, you have to remember the material or solve the problems without your notes, so you should practice doing this before the real thing. It’s ok if you mess up or get it wrong during studying - that’s the whole point. There should be no concern in your mind at all as you walk into the exam because you should be able to remember every single thing that you think could be on it. Focusing on quizzing and testing yourself will get you to this. Don’t just read about a topic, try to remember as much as you can first, then double-check yourself. Try to solve any problem on your own first, then look stuff up only as you need to. This will feel more difficult at first but is most effective overall and will actually end up saving you study time.
For information on the science of learning, check out this website. In my opinion the order of importance is - Retrieval Practice, Spaced Practice, Interleaving, Elaboration, Concrete Examples, Dual Coding. Basing your studying around these will let you learn more in less time. In case it helps build some confidence within you, I got into one of the world’s best universities (around 13% acceptance rate) and used these study techniques to climb from the dumbest to one of the most knowledgeable in my class while also doing music and being a martial arts club president, and maintaining a social life. I realize that university entrance exams can be brutal in Asia, but if you summon a demon to assist and study smart you should be fine.