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.
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.