//use this filter to change the label of the "Select Category" label in the category filter in listings

add_filter('wpgmp_text_settings','wpgm_category_label_change',1,10);

function wpgm_category_label_change( $category_label ) {
$category_label['select_category'] = 'Select Department'; //insert any category label as per your need
return $category_label;

}