Annapurna, the correction window has opened from January 15th and will stay open until January 31st. This is a one time facility. It is not clear as to why you are not able to make corrections. Please try this way: Login to the official website: ntaneet.nic.in with your NEET registration number and Password. Now click on " Correction in NEET application form" and make the desired changes to your application form. Any correction pertaining to the photograph and signature of the candidate will be intimated through e-mail/SMS and the same will be available in the candidate’s login account. Rest of the fields like Father's name, Mother's name, Date of Birth, Category, Gender can be changed during the correction window. Once the correction window has been closed,  NTA does not guarantee that any request for change in information will be entertained. So it is the best thing to make a note of all the corrections that you need to make when the correction window opens from January 15th to 31st and click on the "Final Submit" only after making all the changes that you want to. Once you click on "Submit", enter the OTP number and take the print out for future reference. If it still doesnt work, please reach out to the helpline at their email id: neetug-nta@nic.in