If you are unable to do register in jee main then this article must be helpful for you.

Jee main organised by jeeb and the online application form handled by nic.in which generally use to get data from private mode or incognito mode.

So you first open an incognito tab then open it and fill up the form as per required data. Keeping in mind that it has a session if once your session is over you have to close the tab and again open it in incognito and proceed