My registration form is wrongly filled by myself. How can I correct it?

Dear Student, 

First of all you must provide the entrance exam type for which you have filled the form so that I can tell you the exact solution. For the majority of the entrance examinations that are conducted in the current scenario, there is a provision of correcting the registration form if there have been any mistakes but that can be done only during the time when the correction window opens for that particular example. One must keep looking at the official website of the concerned examination to check for dates of the correction window.