ninja-forms-example-admin-settings-save-setting.php

<?php

function save_example_setting( $setting_value )
{
    if( strpos( $setting_value, '_' ) ){
        $parts = explode( '_', $setting_value );

        foreach( $parts as $key => $value ){
            Ninja_Forms()->update_setting( 'example_part_' . $key, $value );
        }
    }
}
add_action( 'ninja_forms_save_setting_example_setting',  'save_example_setting', 10, 1 );