I need help studying

Iam the smart guy of the boys in my class and another girl I will call Alissa me and her always got good marks we never rally talk but we both got behavior achievements 5 times every year in the 5 years in this school (in my country you need to be 18 to go to collage and school is longer) but after some time my grades started to drop from 99.7 to 98 to 97 to 89 and such And I can't seem to be able to focus alone and I need someone to study with but I don't really have one and all I do is focus on video games I tried to stop and focus on studying and my other friend who is also smart who has been in the school longer than me plays Video games a lot too but there is a difference between us he can focus and understand things easier but I have a hard time and he can stop focusing on video games and start focusing on studying and idk what to do I asked him for advice he said just try to focus I have been in multiple accidents and I think I have something with my Brainn but there isn't I stopped blaming my injuries for me not being motivated to study but I still can't study correctly Can someone tell me tips on how to study and focus and be motivated and to learn and understand easier and to not be discouraged or distracted because i really need it or I won't be able to go to college unlike my sister