Dear Priya, you haven't mentioned the exam you are talking about. Few entrance examinations offer correction windows during which you can change your registered email id. For those examinations, you can change the Email id. But for few exams thete is no correction window. If you have given another Email id than the one you wanted, you should try using it atleast until the counselling for that exam is over. However if you have entered your Email Id wrong like with spelling mistakes as such, you might have to either re-register or write to the authorities because for almost all the Entrance examinations, the mode of communication is online and its important you have a correct Email Id registered. 

If wrong email ID is submitted then a person won't receive the notifications about the respective exam. 

For whichever form if email ID is entered wrong then the person has to wait for the correction window to open of that respective exam. When correction window is open you must correct it in the given time. 

If you still have any queries feel free ask in the comment section down below.