The special round of admission is conducted by the college when the seats of the college remain unallocated. Usually, after the 7th round, most of the seats of the colleges get filled, only the students who are not satisfied with the branch leave the seats and it becomes vacant.
These leftover seats go for the special round and it may be of any branch and you should be ready for that. If you are applying for a special round there is a probability that you will get selected. But you will have to accept the branch as allocated to you.
Keep checking the website of the college if the college is conducting any spot round. You will have to fill the application and do all the formalities for applying in the spot round. Since you have scored 55000 ranks, your chances of getting selected in IIIT Guwahati are quite good as the seats got increased from 89 to 180.
Don’t choose CSE branch to choose multiple branches, your chances will get higher for selection.