You have got a good rank in JEE MAINS and with your reservation you could definitely get CSE in NIT Silchar. For that you will have to register for JoSAA 2019 which is beginning in the third week of June. The latter process is just setting preferences according to the college and course you want and a seat will be allotted to you according to the cutoffs. Just follow the process carefully and you would be good. 

All the Best for your admission, hope you get the college and the course that you want.