If you are using the_field() for a checkbox field. A checkbox field is an array and when you use the_field() ACF will concatenate the values using
$value = implode(', ', $array);
If you want a checkbox field formatted in a specific way then you need to use ‘get_field()’ and do the formatting yourself
// example
$values = get_field('checkbox_field_name');
echo implode(' ', $values); // us only a space
