There are a few ways to improve in your weak subject. For me, the easiest way would be to reach out someone who has that subject as a strength and learn from them. This can be mentoring in person. The other way is to find books or places online that teach the subject, potentially in a different way than you are getting from your current teachers. The challenge here is probably that you are not learning the subject in a way that is accessible to you. Do not try to solve the issue on your own. Reach out to various resources so that you can get ideas from others. That is really the only way to change.