there are free online lectures out there like MIT open courseware, i’ve rewatched some classes that i got fuzzy on. Also specific concepts may be better explained on youtube by like organic chemistry tutor or 3 blue 1 brown.
I have not paid to retake a class though.
After seeing the one where they slam Dan’s face with a ball and you see his skull moving under his skin I realized there can be entire fields of study around insanely fast cameras. What we see in real time doesn’t even compare. Also the one where Gav shows how CRTs work is still my favorite.