@arthurkajaree once you've set up your shop categories, you can add them to your current listings using the bulk editor. On your active listings page here: Manage active listings - eBay Seller Hub, tick all the listings that you want to add to a shop category then click on Edit Selected in the Edit dropdown. That will open them in the bulk editing tool.
Tick them all in the bulk editor then select Category in the Bulk Edit dropdown. You'll then get a popup with sections to change both the ebay categories and your shop categories. Select your shop category there, click Apply then Submit.
