hello student,

For surrender and participant round in Central seat allocation board or csab counselling, you only can restrict your offered choice and can delete some other choices. After allotting your choice, there will be three options what is for seat acceptance(freeze slide and float), and another one is for surrender allotted seat and participate in next round counselling. And you have to go for that. Click on the link below to have a brief idea about

https://www.google.com/amp/s/engineering.careers360.com/articles/csab-special-round-for-nits-iiits-and-gftis/amp