The vacant seats reserved for st SC and PWD candidates will be allotted to candidates of respective  categories for admission to a prep course of one year duration. 

Admission is given to candidate if the seat resevedr for the same category he or she is in is vacant or the canducand has not accepted a prep course last year . 

If he passed the course he will be given direct admission next year in the same branch.

He can again give jee advanced too if he fulfills other criterias

Check the josaa rank lists of last year for idea about closing ranks