There would be capital gains on sale of your flat last year, which are chargeable to Income Tax. You can claim exemption from capital gains tax if you invest specified amount in specified assets within stipulated time. Section 54 requires you to invest in a new residential house and to temporarily park your funds in a designated bank account, you have time till due date of filing return to claim exemption. Alternatively, Section 54EC needs you to invest capital gain amount in specified bonds of NHAI or RECL within 6 months from sale of house. Please go through these sections in detail to know terms and conditions applicable to avail exemption. I strongly recommend you to take professional advice on this so that the advisor can guide on the basis of all the facts.
If you do not avail any of these options, your capital gains will be taxable and you cannot get refund of TDS deducted. However, on the basis of your actual capital gains, you can claim credit for TDS deducted in your return (also cross check this with your form 26AS) as tax paid. If your total taxes paid are more than total tax liability, you can claim refund of the excess tax paid.