Hi DW46!
I understand that you need to assign workers' compensation to an item or service. Let me share some details about it.
In QuickBooks Desktop, we can add workers' compensation code but we're unable to tie it to a product or service. Also, you've mentioned that you're using a time tracking app. You'll want to reach out to their support and see if they have a different way to map those codes.
If you need a report or help in setting up workers' compensation, please check these links:
Keep on posting here if you need anything else. We'll respond as soon as we can.