Hello Subrata,

Well you can participate in CSAB NEUT round but only after JoSAA counselling ends. CSAB NEUT round is only for candidates belonging from North-Eastern States & Union Territories. Below I have provided the important dates regarding CSAB - 

• Application form is available from 28th June to 6th July.
• Verification of documents will be done from 28th June to July 8th.
• Filling of choices will start from July 10 and will continue upto July 17
• Seat allotment for round 1 is in 19th July and reporting for the same is from July 20 to 24.
• Seat allotment for round 2 is in 26th July and reporting for the same is from July 27 to 31.
• Candidates can withdrawl their seats from August 1 to 3.
• Spot rounds will be declared by the state centres by august 5 to 8.
• Reporting at the admitted institute will be done from august 9 to 14.

CSAB NEUT Seat Allotment : 

• Registration : The candidates ahve to register using their JEE Mains 2019 application number & password.
• Choice Filling & Locking : Candidates have to fill up their choice of colleges & branches as per their preference. 
• Allotment of Seats : The authorities will allot seats to the candidates based on the candidates rank, choices filled & locked and seats availability.
• Reporting and Document verification : Candidates with allotment letter will have to report to the respective reporting centre with all the required documents for verfication purpose and would also have to pay the counselling fee.

You can also go through this link and checkout the detailed process for CSAB NEUT : https://engineering.careers360.com/articles/csab

Hope this helps you.Good Luck !!!!