Oat Study Advice

Hello everybody, I am currently working up to taking my OAT this October and need some advice on studying. I wanted to see if anyone had any tools they recommend using that might be more geared towards starting from scratch. I do have background knowledge on the subjects but really struggle with my chemistries and such. Any advice would be greatly appreciated. I’ve been looking into OAT booster and am wondering if it’s really a good option for this, especially for its cost.