Rectification or revised returns after assesment under section 143 (1)

I HAVE RECEIVED A INCOME TAX INTIMATION UNDER SECTION 143 (1) WITH TAX DEMAND OF RS.46,000...I HAD FILED THE OPRIGINAL RETURNS WITH ERROS AND AGAINED FILED TEH REVISED RETURNS WITH ERROR THAT I HAD NOT TAKEN HRA AND CONVEYNACE ALLOWANCE EXEMPTION..NOW THE ASSESMENT HAS BEEN DONE..I WANT TO REVISED OR RECTIFY THE SAID RETURNS AFTER TAKING CONVEYANCE AND HRA ALLOWANCE..HOW DO I DO THAT ???