There is no quick fix.
I suggest taking up some form of meditation, it has helped me.
Like Paddestoel has said, you can't expect a tangible change over a very short time. Chess is a good exercise to develop the ability to sit down and stay focused and concentrated for a long while.
Reading also helps. Start with something that interests you, like novels or science magazines or whatever.
Devote daily time to such activities, turn them into your routines and make sure you get some time away from the internet, tv or smart phone. Taking daily one hour walks is also good meditation.
10 concentration exercises
I hope this has helped you
I also have trouble reading/ studying. Maybe something is wrong with my cortex. :(
How can I make my brain healthier/ stronger in a short amount of time?