You can start your study online, As you get proper knowledge about your std 12 as well as jee mains. Now the online classes has been started, you can study from that also.You can also download pdf.There are many ways to crack JEE. First of all try to solve last years papers and more question which can improve your marks.

Thankyou very much!

Hey there

We know it's a hard situation for you but you have ample time left. Also you can utilise this time of lockdown to study online. Careers360 has India's best faculties and this platform provides you complete course for jee mains. I can assure you that you'll definitely crack the exam if you use this platform sincerely.

I am providing you the link

https://www.google.com/url?sa=t&source=web&rct=j&url=https://learn.careers360.com/knockoutfull-jee-main-april/&ved=2ahUKEwjR34ia5ZzpAhXKAnIKHb7gAGMQFjALegQIBRAB&usg=AOvVaw3AbUupAhvQ-6JAbKBbKNx5&cshid=1588683727657

Good luck