To remove text from the Text widget, you can use the delete method:
$text->delete(index1 [ , index2 ]);
The first index argument is required, but the second is optional. If both are specified, the first index must be less than or equal to the second. All the characters from index1 to (but not including) index2 are removed from the Text widget. If you want to delete everything from the Text widget, you can use $text->delete("1.0", 'end').