Income tax refund

I had filed income tax return of my Father on which tds was deducted and it was to be claimed refund. However the return was filed after due date and whereiin while data entry i made a typography error in TAN Number of Deductor due to which the amount of refund reduced from 10000 to 4000. I want to know whether the difference amount can be claimed? If yes then what is the procedure for the same? How much time would it take for the same?