Hi Aspirant,

There is no need to worry. If you have appeared for JEE-Main January session then you have to login through credentials of January session. You don't need to signup again as a fresh candidate.

If you are appearing for JEE-Main exam first time then you have to Apply for fresh registration.

As you said that some of the details are filled by you so you might have got your application number and application form has been saved but not submitted yet. Now after getting application number you can login through you application number and password set by you.

Hope this helps you. For further doubts feel free to ask here.

All The Best!!