Close  Act and Outlook. Open a secure Command Prompt as administrator , start/cmd/right click on cmd.exe and choose Run as Administrator – or in Windows 10 choose Start Command Prompt – Admin

Change to the folder where Act is installed cd C:\Program Files (x86)\ACT\Act for Windows

Type regasm actoutlookaddin.dll and click enter.

Type gacutil /i actoutlookaddin.dll and click enter.

Reopen Outlook and the addins should be there.