Hi

Please ask a more specific question. Well still let me share some information about CSAB Spot Round and JoSAA Special Round.

JoSAA conducts Special Round for students who have already been allotted seats. But through this process they have a chance to get any other preferred branch in the same institute. 

But CSAB Spot Round is for those who haven't been allotted any seat. And no withdraw option.

Best of Luck.

Hope this helps.

Cheers!