i. Go to Set-Up → GRN
ii. Click on ‘Add Simple GRN’ button from tool strip
iii. Select the item. You can change the details like purchase price, purchase tax, etc as per requirement
iv. Select the item added in grid and click on ‘Apply Discount On Items’ button from tool strip.
v. You can select the ‘Discount Flat’ or ‘Discount Percent (%)’, enter the discount being given and click on ‘OK’
vi. You can repeat steps iv and v also for other items added in grid.