Hi Lucy,
Thanks for going PRO and we are surely happy you love it! Let me try to help you with your question.
You will need to add a little bit of code to your functions.php file.
(Note, that using a child theme is recommended. You can find more info on child themes here.)
So in your admin go to Appearance > Editor.
On the right side you should see a list of files. Click on functions.php to have that in the editing window.
Add this piece of code to the file and hit Update File.
add_filter( 'tribe_events_register_organizer_type_args', function( $args ) {
$args['rewrite']['slug'] = 'teachers';
return $args;
} );
In case you don’t have a child theme and you add it to the functions.php of your main theme, then the changes will be lost when the theme is updated.
Let me know if this helps!
Cheers,
Andras