Most of these functions to not have documentation, you need to dig around in ACF code. After the field group is completely set up, get the field group.
$group = acf_get_field_group[$group_key];
then get the fields for the group
$group['fields'] = acf_get_fields[$group_key';
then write the field group to a file
$filename = '/aba/path/to/your/file.json'
$handle = fopen($file, 'w');
fwrite($handle, json_encode($group));
fclose($handle);
then you can download this file from the server and import it to ACF.
