Values separated by comma to filter - PHP - Wordpress

I'm trying to separate values with a comma within a custom field so that the plugin I use from filters can separate them.

The custom field is called 'sub_ubicacion_norte' .

The values are for example in a post: "San Isidro, Vicente Lopez, Pilar".

Now in the filter I get "San Isidro, Vicente Lopez, Pilar" as a single option and I want it to be three in this case.

The code I am embedding in functions.php is:

function my_acf_update_norte1( $value, $post_id, $field) {

$field1 = get_field('sub_ubicacion_norte');
var_dump($field1);


$norte1 = substr($field1, 0,1);

var_dump($norte1);

return $norte1;
}
add_filter('acf/update_value/name=sub_ubicacion_norte','my_acf_update_norte1', 10, 3);


function my_acf_update_norte2( $value, $post_id, $field) {

$field2 = get_field('sub_ubicacion_norte');
var_dump($field2);


$norte2 = substr($field2, 1,2);

var_dump($norte2);

return $norte2;
}
add_filter('acf/update_value/name=sub_ubicacion_norte','my_acf_update_norte2', 10, 3);