Can I specifically review old sections?

Heyo, welcome back to WaniKani!
Perhaps you are looking for the option to reset to an earlier level? You can find this by going to Account → Danger Zone. I’m not sure about the ability to reset individual items (there is a burn manager script, but you can only reset burned items with it as far as I know), but self-studying with scripts is an alternative option to level resetting, and can be done with scripts found here.