If the error is only date on the photo, you need not worry because that will not be the reason why your application will be rejected. But speaking generally, for any other mistake, once you filled the application and submitted the application, then you did not make changes to your application form. There is no correction window for SSC CHSL examination application form. But if you did not submit the application form, then you can re upload another photograph this time correct. But if you submitted the application form, because you cannot make changes, the only other option is to re-register with a new mobile number and email id and fill in another application form. But if it is only date that is missing, it is ok. Your application will not be rejected.