Hey Vinnu.

See for applying the JEE MAINS form for April session u must have registered to the mains portal. In the January session u have been provided with the credentials.

Since u are not able to access the account then there is option to recover or access ur account on the lower right side. If even by doing that u are unable to access then contact the managing committee for help as soon as possible. 

Hope u got ur point and contact them with proper explanation about the problem u r facing.

Good luck