Hello Subhi,

You can apply for it on the official CBSE website.

Key points are -

• You should have passed in all the subjects (otherwise you need to apply for re-appearing instead of improvement).
• The application can only be done online. The last date without late fees is 27th Nov (with the appropriate late fee, the last date is 26th Dec).
• The fees per subject are Rs 200 in India and Rs 1000 abroad.
• If you are a 2018 student, all your details will be fetched automatically.
• If you passed in 2017 or earlier, you can still appear, but you’ll have to provide all the details (this is important for2nd-time droppers for JEE Main)
• IT IS NOT MANDATORY TO APPEAR FOR ALL SUBJECTS (even if you plan to appear for JEE Main as well). You can (and should) choose the subjects in which there is definitely a scope for improvement.

The candidates will get two options to apply for the improvement exams. Those 2 modes to apply for the exams are as follows.

Online Mode

• Go to the official portal of CBSE.
• Now open the link of the improvement exams.
• Fill the registration details.
• Choose the exam centers & subjects.
• Submit the fees or generate an offline challan.

Offline Mode

In this mode, the candidates will be able to apply through the school. They will have to approach the school authorities to apply for the improvement exams.

Hope this helps.