I have to presume you are using either TurboTax Self-Employed or Home & Business. I have a copy of the latter and you start with the Inventory and Cost of Goods Sold section in which you will be asked if you have inventory to report.
One of the first few screens will be boxes to enter beginning of 2019 and end of 2019 inventory. The immediately following screen will have, among others, a box for Cost of Purchases which is where you will input the cost of the inventory you bought.
