PLANT & MACHINERY- INPUT TAX CREDIT. Section 17 5 d Vs Section 18 6 - Goods and Services Tax - GST

Dear experts The provision of Section 18[6] of the CGST Act reads asunder: 6) In case of supply of capital goods or plant and machinery, on which input tax credit has been taken, the registered person shall pay an amount equal to the input tax credit taken on the said capital goods or plant and machinery reduced by such percentage points as may be prescribed or the tax on the transaction value of such capital goods or plant and machinery determined under section 15, whichever is higher: Provided that where refractory bricks, moulds and dies, jigs and fixtures are supplied as scrap, the taxable person may pay tax on the transaction value of such goods determined under section 15. Query: Coming back to the retrospectively amended Section 17[5][d] governing the entitlement of ITC on Plant Machinery, what is the significance and implication of Section 18[6] on such ITC availed under Section 17[5][d]? What the beneficiary of such ITC needs to do? Plz clarify.