Hello Hima,

I am assuming that you have filled the application form for some undergraduate program admission and have filled the wrong hall ticket number while filling out the application form. If so, then in case of online applications, most of the authorities provide a correction window in which you have to correct this, else you can also mail them with your registration number, name and the correct details and request them to consider and correct your mistake. If the form was filled online, then I am sorry but there are very little chances of you having a chance to correct the details. 

If the details are not corrected, you will face a lot of problems and even your candidature may be cancelled.

One alternate step, though it should be the last one would be to fill another application form with different contact details like mobile number, email id, etc and the correct details.This won't lead to multiple submission problem as the hall ticket number in both cases would be different.