I did a search on PSC for posts that look to be related to your issue. I believe that you must install Office support when you install Studio. This is required. The connector is found in the Pega Robotics Connectors section of the Toolbox.
If you did not select the correct Office version during installation, you will need to uninstall, restart your machine, then re-install Studio. If they still do not show, you can manually add them from the OpenSpan.Office.dll.