For Act! versions 2005 to 2013, Act! didn’t make it easy create company records and link multiple existing contacts to them after an import or conversion from legacy Act!.  This guide below shows you how to do this if you have these versions of Act!.

Alternatives;

  1. Upgrade to v16+ of Act!
  2. Purchase this utility that converts existing data.

Here is a guide if you don’t want to upgrade or buy the plugin.

http://www.mondocrm.com/wp-content/uploads/2017/07/MondoCRM-Create-Companies-from-Contacts-Guide.pdf