Take a product that already sells, keep its garment, factory, size range and pricing, and change only the artwork and the words. This is what makes a coherent store rather than a pile of unrelated tees.
The steps
POD — another one like this runs source → copy → seo → New artwork? → upload → variants → areas → approve_create → create → save.
Who can run it
POD — another one like this reaches an instance's own resources, so it runs on an operator's Leumas Studio; open it here to read and adapt it.