Hello There,

For any Counselling and Allotment of Seats you need to follow some rules strictly step by step.

As you asked, for choice filling you must have been registered yourself to be appearing in the counseling.

For Online Filling and Locking of the Choices , you must search for the desired colleges and fill the choices as per asked in the website. Once all the choices are filled, you must lock and submit the choices and preferences before the last date ends.  After completion of a round you can again fill your choices.

Hope it Helps :)