On the Back Office : Exporting existing products and options from a store
Go to the store Back Office Product Page and click Export CSV
Name the CSV after the store name
On Excel : adding SKU on products and options
Open the CSV on Excel
Manually populate SKU Column with required SKU for each product and option
Export the tab in CSV with semicolon as separator
On the Back Office : updating products and options with SKU
Go to the store Back Office Product Page and click Import CSV
Select the generated CSV of the store
Click OK
The store products and options are updated with SKU