Update the purchase price of the item (product) when a quantity purchase is made from Purchase Orders in zoho Books.

Update the purchase price of the item (product) when a quantity purchase is made from Purchase Orders in zoho Books.

Update the purchase price of the item (product) when making a purchase by quantity of Purchase Orders in Zoho Books.

Good afternoon. I would like to know how to update the prices of my products with the purchase orders from zoho books.
Example: when buying the quantity of 10 products at 8 dollars (purchase price) each with a total of 80 dollars, but in my already registered products the sale price is 7.60 dollars each, with which when making a sale in the system you would be losing $ 0.40. Could you help me with a solution?