UPSC usually opens a correction window after the application closes — watch the official UPSC website for the dates.
Log in to the UPSC application portal and open the correction link to re-upload your photo or signature.
The photo and signature must match the size, format and background rules given in the notification.
Only the fields listed in the correction notice can be edited, so fill the form carefully the first time.
If no correction window is announced, contact the UPSC facilitation counter with your application details.