getting id of item in custom list

I am creating an entry (CustomListCustomValue) in a custom list. How do I get the id of the the new custom value (not the list itself)

var customRecord = new CustomList
{
internalId = customListRecordTypeId,
customValueList = new CustomListCustomValueList
{
replaceAll = false,
customValue = new[] { new CustomListCustomValue { value = customListValue } }
}
};

var response = RetryPolicy.Execute(() => _netsuiteService.WithTokenPassport(_configuration) .update(customRecord));