>Also where in that field should I place the code described here: https://unacms.com/wiki/Dev-Uploaders

In this your case, it means to edit the file with the module's form - modules\boonex\organizations\classes\BxOrgsFormEntry.php

But this is not good to edit the default files so it's better to have own module which will have own upload form. It will have the service methods to draw the add / edit form which you will paste to any necessary place.