Shopify inventory upload

Question

I'm working on a case where I have to upload new products to the Shopify inventory, but the data seem to me arranged without logic.

I have the Shopify file (let's refer to it as ShopifyExport.xlsx) that I get exporting the inventory, which has as header:

`Handle,Title,Body (HTML),Vendor,Standardized Product Type,Custom Product Type,Tags,Published,Option1 Name,Option1 Value,Option2 Name,Option2 Value,Option3 Name,Option3 Value,Variant SKU,Variant Grams,Variant Inventory Tracker,Variant Inventory Qty,Variant Inventory Policy,Variant Fulfillment Service,Variant Price,Variant Compare At Price,Variant Requires Shipping,Variant Taxable,Variant Barcode,Image Src,Image Position,Image Alt Text,Gift Card,SEO Title,SEO Description,Google Shopping / Google Product Category,Google Shopping / Gender,Google Shopping / Age Group,Google Shopping / MPN,Google Shopping / AdWords Grouping,Google Shopping / AdWords Labels,Google Shopping / Condition,Google Shopping / Custom Product,Google Shopping / Custom Label 0,Google Shopping / Custom Label 1,Google Shopping / Custom Label 2,Google Shopping / Custom Label 3,Google Shopping / Custom Label 4,Variant Image,Variant Weight Unit,Variant Tax Code,Cost per item,Status

`

The header above are what Shopify wants in the CSV file that I will upload, for what I can understand.

Now, the problem is that the supplier sends inventory data with a file that has three workbooks. The three workbooks have the following data:

Within SupplierData.xlsx, Workbook1:

Description, Color, Size, Cost price, Sell Price on Shopify, Sell Price On Other Marketplaces

Within SupplierData.xlsx, Workbook2:

Item Barcode, Description, Price, Preferred Vendor, Composition, Weight (GR)

Within SupplierData.xlsx, workbook3:

Brand, Reference, Product name, Description, Composition,   Sales description, Video Link

Now, my question is, how do I add lines to ShopifyExport.xlsx adding those products? My goal is to write on ShopifyExport.xlsx, which include what was already there and the new products introduced by the supplier.

It seems to me like a puzzle, as every piece is in a different file and in a different place. Also, note that all the files cited above are not of the same length. For example, the file that cites the sizes has more parameters than, for example, the price. Given the same barcode, the price is the same, regardless of the size.

I hope I explained it clear enough and if anything is not clear please let me know.