Try to solve the problem/challenge without it. When you start feeling that hard part, that difficulty, make a note of it and dig into that and search for what knowledge you're missing, some course, some chapter. Then repeat.
You have to do recovery work. In the past, students used to be "held back" to repeat courses or entire years. That was a good thing, they had to try again to get it right. Now, the educational system is afraid of doing such things, and it's even afraid of giving failing grades, which means that you're not getting that necessary feedback. So it's on you now to give yourself the negative feedback, to evaluate yourself, and to try again. It sucks, I know.