NOTE: It's recommended for you to have backup of the database. Solution is tested with JomSocial 3.2.1.4
Overview
This solution will allow you to assign one multiprofile to ALL users that remain with "Default profile"
Instructions
1. Login to your database via PHPmyAdmin.
2. Make copy of your database.
3. Click SQL button in upper menu.
4. Run this query:
UPDATE `name-of-your-database`.`your-table-prefix_community_users` SET `profile_id` = 'xx' WHERE `profile_id` = '0';
Change:
name-of-your-database = your database name
your-table-prefix = your table prefix
xx = id of multiprofile that should be assigned to ALL users having "Default profile"