Itc reversal on credit note u/s 43

Kindly guide me on the procedures for reduction of ITC cliam by registered person U/s 43(1).. i.e..,how a cement dealer should reverse the ITC for the discount received through Credit note raised by the cement company in the GST returns.is it correct to reduce the Amt of GST  on Discount received from the ITC eligible while filing GSTR-3B.

Thanks.