Joomla - Hika User synchronization

-- HikaShop version -- : 2.3.4 Business

How and when does the user synchronization occur ?
Here is my scenario:
Main registrations on the website are done through Hikashop user registration form.
However I have another 3rd party form, that is also adding users in jos_users, both in front-end and backend. This is required for a few other features of the website...
I noticed though that those users are not added into hikashop.
Is the hika plugin able to synchronize the hika_user table with data from the jos_users table ? When and how is this happening ?
Or I should take care the creation of new hika_user with the submission of my other form?

Upon the creation of a new user, the hika_user table is automatically updated and contains the new user. But I haven't found any way to sync hika_user table with records already existing in jos_users. Is this possible?

Thanks Nicolas!
Yep, that's exactly the case - I had imported records directly from the database and this how exactly I figured this out after studying the hika_user table. I run an SQL insert query containing the jos_user.id and the jos_user.email fields of the records.

Here is a sample of a complete INSERT query syntax for the hikashop_user table, for anyone who might need something similar:

INSERT INTO `jos_hikashop_user` (`user_id`, `user_cms_id`, `user_email`, `user_partner_email`, `user_params`, `user_partner_id`, `user_partner_price`, `user_partner_paid`, `user_created_ip`, `user_unpaid_amount`, `user_partner_currency_id`, `user_created`, `user_currency_id`, `user_partner_activated`)
VALUES

('', 3387, 'This email address is being protected from spambots. You need JavaScript enabled to view it.', '', '', 0, 0.00000, 0, '127.0.0.1', 0.00000, 0, 1417187337, 0, 0),
('', 3388, 'This email address is being protected from spambots. You need JavaScript enabled to view it.', '', '', 0, 0.00000, 0, '127.0.0.1', 0.00000, 0, 1417187337, 0, 0);