Dear Nihal, you can reach out to the Tahasildhar of your state if you want change your Category from OBC to General and they will do the needful. However, you cannot change anything on the markslist once it has been issued. If you do not want to avail your category, get a certificate from your Tahasildhar and they will issue you a certificate. This can be sent to the concerned authorities for the future. But for the times you have availed the OBC benefits, you cannot go back in time to get it changed.