The Google fields can be updated with Stock Sync by using the metafields.
Google Fields | Metafield namespace and key |
Google Product Category | mm-google-shopping.google_product_category |
Gender | mm-google-shopping.gender |
Brand | mm-google-shopping.brand |
MPN | mm-google-shopping.mpn |
Size | mm-google-shopping.size |
Color | mm-google-shopping.color |
Custom Product | mm-google-shopping.custom_product |

To know more about metafield click here.