If you want to simply add additional rows of data to increase your test coverage, you can create a new Excel Spreadsheet (or Google Sheet) with just the additional rows of data, save the new file as a CSV file and use that file to “append” the data in the grid.

Once you have the append data CSV ready, just click “Append Data” button at the top of the data grid when in Edit (WIP) mode of the Data File, and upload the CSV file.