Now that you have built the format, take the supplier file and remove all but 1 row to create a test product file and save it to your desktop. Ensure you keep the file as a CSV file.
Within ecomdash, go to the Quick Links dropdown on the top left hand side of your screen, and take the upload inventory action. From there, select the file, select your new format you created and click the upload action. You will want to confirm once the file has been processed that you see the product uploaded within inventory and that all of the data has been mapped accordingly.
If you see any fields not mapped correctly, you will want to revise your mappings in your format and run another test until you are happy that you have the fields where you want them.