You should be able to record the existing inventory that you have onhand. While I’m not familiar with Etsy, I’m sure there has to be a way to establish your inventory cost and quantities that you previously purchased. You may want to contact their support team to see if they can assist you.
If you are trying to establish inventory in QuickBooks, you can enter your existing quantity and the cost when you create a new item. Below is a video tutorial on how to do this: https://fitsmallbusiness.com/set-up-products-and-services-list-quickbooks-online/.
Best of luck,
Crystalynn Shelton, CPA