This requires administrator rights in Planner
The users can download an installationfile to install Planners Outlook add-in on a local installation of Outlook under "my settings" in Planner.
But first the Planner administrator has to enable the installation files.
Go to "Settings"
Click "Other settings"
Scroll down to "Outlook installers"
Here you can create the installer that matches your users. There is a difference between a 64-bit installer and a 32-bit installer. The "Outlook Add-In 2016/Office365 for Pronestor" installer is a 32-bit, and so are all installers without 64-bit in the name.
You might need to enable multiple installers if your users use different versions of Outlook.
Q. How do I download the created msi?
A. See this guide https://helpdesk.pronestor.com/hc/en-us/articles/360036192531