I am extremely story to tell you dear but now you can not fill JEE mains 2020 second session application form
This is because,
The last date to fill JEE mains 2020 application form has already passed
Your JEE mains 2020 second session application form was released on 7th February 2020 and the last date to submit application was 12th March 2020
But It was again re opened on 19th may and last date to fill the form was 24th May 2020.
So, the last opportunity to fill JEE mains 2020 application form was 24th may 2020 which has passed and thus you cannot fill it now.
So , the only option left is to wait for JEE mains 2021 if you want to appear in JEE Mains
sorry to say but now you cannot apply for the JEE mains exam as the application form was out from february 7, 2020 till march 12 2020 (5 pm) and the last date for JEE main application fee payment was also 12 march 2020 (11:50 pm)
better luck next time!