You edit a filter group by clicking the filter group name. This brings up the Edit Filter Group page in the same window. You can click the Add button above the table bring up the Add Filter Group Entry popup. When you finish adding an entry, the data is added as a new table row.

You can click any link in the MIME Type column to bring up the Edit Filter Group Entry popup to modify the data contained in that row. You can delete a row by selecting the row and clicking the Delete button above the table.