Thank you for reaching out to the Community! I’m happy to provide some assistance with adding variant options to the shop, to get this resolved. As you’re looking to sell by both piece and set, I would recommend checking out the Shopify App Store for a list of available product option apps. For ease, I’ve gone ahead and suggested a few below you can look into:
Alternatively, you can look into hiring one of our Shopify Experts to have this customized as noted by @Dbuglabpvtltd . Our experts are trusted third-party agencies or freelancers that offer various services to help build your business. For more information, you can check out our Expert Marketplace.
Please let me know if you have any other concerns.