You have to take participate in speacial round organised by CSAB.You have to pay the reuired fees to participate in the special round .Then you have to make a new choice list according to your choices for special round.There isnot any reservation in special round.You will be refunded if you dont get  a seat in special round ,it is compulsory to take the seat ,if you alloted a seat in special round.If you get a seat in JoSAA couneslling ,you will be asked about your willingness to participate in the special round in the admission time in that college.