Hi carin,
you need to insert an entry, for each user, in the tables:
- #__cck_core
- #__cck_store_item_users
For #__cck_core
INSERT INTO `o03b4_cck_core` (`cck`, `pk`, `pkb`, `storage_location`, `storage_table`, `author_id`, `author_session`, `parent_id`, `store_id`, `download_hits`, `date_time`, `app`) VALUES
('user', 232, 0, 'joomla_user', '', 232, '', 0, 0, 0, '2021-04-12 06:57:28', '');
Where `pk` is the ID in the table #__users
For #__cck_store_item_users:
INSERT INTO `o03b4_cck_store_item_users` (`id`, `cck`, `gender`, `last_name`, `first_name`, `about_me`, `avatar`, `address1`, `address2`, `city`, `postal_code`, `region`, `country`, `phone`, `website`, `birthdate`, `birthplace`, `company`, `company_vat_id`) VALUES
(232, 'user', 'M', '', '', '', '', '', '', '', '', '', '', '', '', '0000-00-00 00:00:00', '', '', '');
Just replace 232 by the ID of the user.
Regards.