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This is done by opening an Office program, e.g. Word, going to File → Account, and logging in there, with an account that is part of the organization the plugin was distributed to.
Once all this is done, restart all open Office programs. Start word again, and a button "digizuite" should now be available under the "insert" menu in office. If not, the plugin might have to be activated once, by selecting "My Add-ins" from "Add-ins" under "Insert", and selecting the Digizuite Office Connector from the "ADMIN MANAGED" section.