NIFT second round of councelling is very similar to first round. You’re called rank wise to change your center or course if you want to or if there are vacancies available.
The seats vacated by students before you will be immediately available for you to grab.
Suppose, a person with rank 200 from Hyderabad leaves a FD seat, then that NIFT Hyderabad FD seat will immediately be available to 201st ranker(if he/she has applied for second round of councelling) or the immediate next person after rank 200.