Fine what are those proper fields, I have imported my products already. Also I have uploaded my unit of measures as well but they should be applied to each specific product. How that can be possible?

You should govto the products page and then press import and select the proper fields

Then press test to check that everything is ok,then import to update the upm in products.

If you got the excel from the system by exporting the products or you predefined your external ids when creating the products in the first place,the above will work just fine.

You should choose external id while updating otherwise it will create new products