Editing Schema file in BigCommerce Cornerstone Theme

Question

Google Merchant does not recognize my product size variations. The micro data that Cornerstone theme is generating is not display the different sku and price. I tried using Schema App but they can not edit theme files. I am struggling with where to edit the schema.json files. I believe I know what to add but can not find how to edit the files. This is the code I believe needed:

{
  "@context": "http://schema.org/",
  "@type": "Product",
  "name": "Clarks Falalala Shoes for Men",
  "image": "https://example.net/shoes/clarks-falalala.jpeg",
  "description": "A great comfortable walking shoe, carried in sizes 9-11, but now size 11 isn’t in stock",
  "offers": [ {
    "@type": "Offer",
    "sku": "QWERTYSHOE-9",
    "price": 45.99,
    "priceCurrency": "EUR",
    "availability": "InStock"
  },{
    "@type": "Offer",
    "sku": "QWERTYSHOE-10",
    "price": 45.99,
    "priceCurrency": "EUR",
    "availability": "InStock"
  },{
    "@type": "Offer",
    "sku": "QWERTYSHOE-11",
    "price": 45.99,
    "priceCurrency": "EUR",
    "availability": "OutOfStock"
  } ]
}

Please help me with where to edit schema file. Thank you in advance for your help.