edit a csv file

hello ? I'm looking for support in editing several CsV files. I have 2 old files and a new one that has product name , descriptions and other things in it . I need help in processing, in the 2 old csv files are descriptions that I would like to include in the new file, some new products are included. the direct copying does not work, but the barcodes are identical. there are tables with about 9000 products, about half of which match the barcodes. all that match should transfer the description from the old csv to the new one. and when that's done. I should be able to upload the file back to shopify without any problems.