Hello anubhab, thanks for asking this question on this platform.actually when you apply for engineering college then counselling starts in 2 rounds in case of state government college and  when you will get a college then you have to report at the alloted college for further process .thanks 

Hello Dear
After applying for the engineering colleges via any mode jee mains etc. based upon your score and rank obtained in that respective examination they will allocate you the college. After the allocation if your marks are under the cuttoff region then they will prevail you with that respective branch. That is the real play scenario which is going to be happen during the time of counselling.
All the best