This Outlook Add-In can be used with your Office 365 email account to send email invites and or schedule events from within Outlook 2016 and Outlook Web Access (OWA).
This article will guide you through Office 365 Admin Portal.
Log in to your Office 365 Admin Portal
From the left Navigation Select Settings then Services & add-ins
Select Deploy Add-In
Select "I want to add an Add-In from the Office Store"
Search for "vast" in the text field then click on Add
Make your selection and click Next
Make your preferred selection then Save
Once completed, this can take up to 24 hours to appear within your users Outlook.