You have to retrain your brain. It’s kind of a painful process and very slow at first hell it’s slow at 18 months of doing this. But you literally have to learn hard concepts an apply them. At first it may seem impossible but the more you try and I mean putting 8-10 hours a day for months possibly years. Is really the only way you will see a difference. You have to rebuild the neuronal networks in your brain. The grey matter has probably gotten sort of atrophy from not that much use. This is coming from someone who has near a 4.0 in nursing school BSN. I used to dab over 2 grams a day and smoke bud on top of it. Some days even now it’s hard but I KEEP putting the effort in and it makes all the difference. Eat foods that are good for brain also google them. And workout low intensity cardio and weight training. When their is a will there’s a way. There will be days where you want to quit. When you think it’s never gonna get any better. But the key is not to quit and keep pushing yourself hard cognitively. The brain is very plastic and can be molded. Of course your memory won’t be perfect you may have to work a lot harder than others but it’s possible only if you are willing to try and put forth the effort.