Hello Anameeka,

JEE mains is one of the most important examination that students take to get into some of the most prestigious engineering institutions of India. This will open doors for the NIT's, IIIT's and BIT's. So it's understandable how important it is to fill the form correctly. 

Since you have already applied for JEE mains which was held in January you can use the same login ID to fill the form. From this year Jee mains is conducted twice in a year and it is now conducted by NTA i.e. National Testing Agency. It will be conducted online only. 

After the application procedure is closed NTA will open a window to make changes in the application form . For the April session, you can start editing your application form from March 11 to March 15. For this a small fee will be charged and you will be able to make changes in your application form. Your application form should be complete in all respect and only after submitting the fee you will be able to make changes. You have to go to the JEE correction portal and login using your credentials and follow the steps. In this way you can change the details which went wrong when you filled the form for the first time. 

Hope everything is clear to you. 

All the best.