Every time you upload a CSV file to ProductMatrix (v16.11 or greater), Premium MatrixRate (v4.7 or greater) or ShippingOverride (v3.9 or greater) a backup of that file is saved to your file system. This can be found under <Magento Folder>\var\export\your_csv_file_name.csv
Therefore if you have misplaced your CSV file and need to edit your rates just take a copy of this file, edit it and re-upload it to your extension. No need to re-create your CSV file or look in the database.
Note: This example is using Product Matrix.
You need to find the table called shipping_productmatrix and click on it. You then need to find the export tab at the top of the page and select the export as CSV option. Please see the attached screen shot for the correct settings.
You should expect your exported CSV to look like the screenshot below:
When you export the file you will need to remove the columns: "pk", "website" and "cost" from the CSV file.
You will also need to change the region codes back to region names. If there is a "0" in the region column you need to delete this as Magento will see it as an invalid code when uploading.
You should end up with a CSV file similar in layout to the screenshot below: