Hello Simran

Spot round will be held after the completion of admission process for the purpose of filing up vacancies. The registration for spot round will be online as qualifying students of wbjee have to register first themselves online, then pay the registration fees and opt for choice looking. To know more about the same in detail, you can refer to :

http://www.engineering.careers360.com/articles/wbjee-counselling

Hope this helps you !