Open an option set, or click Create option set to start one, and go to Products.
Under Show these fields on, pick All products, Specific products, Products in collections or Specific variants.
Click Browse and choose them.
Click Save.
With Specific variants, the fields show only while one of those variants is selected. If you add products to a collection later, resync them in Settings.
Still stuck?
Open the app in your Shopify admin, go to Help and click Chat with us, or email [email protected] with your store’s myshopify.com address.