Hello aspirant, greetings to you. Special rounds work exactly the same as other 7 rounds. After the completion of the seventh round of JEE MAINs counselling, the registration and fee payment for the special round begins immediately. As for 2019, the  registration for special rounds are scheduled from 24 July - 26 July 2019. 

You can fill the for on the official site of CSAB, along with college and courses of your preference.

Good luck