The required fields for importing new users are:
CSVI checks first if the user_info_id is in the imported file because this is the unique identifier for each address. In case this is not present, CSVI will try to find the user_info_id based on the user_id or email, address_type and address_type_name. When no user_info_id is found a new address will be added, otherwise the existing one is updated.
CSVI will use the shopper_group_name field to find the correct ID to link the user to the correct shopper group. If the supplied shopper_group_name cannot be found the default shopper group will be used.
CSVI will use the vendor_name field to find the correct ID to link the user to the correct vendor. If the supplied vendor_name cannot be found the default vendor will be used.
A Joomla user is updated when the email field is imported.
The username field is not required and if you do not include it, CSVI will use the email address as username field.
There are 2 fields to handle passwords, only 1 should be used for import:
CSVI creates Joomla users if:
If the user_id field is imported, the user data will only be updated.
See the Joomla documentation on how to recover the administrator password.