Like this:
table = event.source.parent.getComponent("Table")
selRow = table.getSelectedRow()
selCol = table.getSelectedColumn()
if selRow != -1 and selCol != -1:
newData = system.dataset.setValue(table.data, selRow, 'C', 'Test1')
newData = system.dataset.setValue(newData, selRow, 'D', 'Test2')
table.data = newData