If the Outlook Plugin is not showing when right mouse clicking on an appointment then the plugin might have become disabled.
Please try below to re-enable the plugin.
1. Click file
2. Click options.
3. Click Add-ins
4. Look for the Add-in that's called "AROutlook2018Addin" or "AROutlook2010Addin"
5. If it's in Inactive click Go down the bottom where it says Manange: COM Add-ins. If it's in "Disabled" change the COM-Addins box to "Disabled items"
6. Find "AROutlook2010Addin" and enable and click okay or if disabled click AROutlook2018Addin and click enable.