Wrong qouting of pan in challan

HI FRIENDS I WOULD LIKE TO ASK YOU THAT ONE OF YOUR CLIENT PAID THE SELF ASSESSMENT TAX BUT BY MISTAKE THE PAN NO. IS WRONG AND THUS THERE IS NO CREDIT IN HIS ACCOUNT. SO PLEASE FRIENDS HELP ME IN THIS MATTER AND HOW I CAN GET THE CREDIT BACK PLEASE TELL THE PROCESS FOR IT THANKING YOU IN ADVANCE