To manually deploy VSight add-in for all users (Office 365 admin), follow the guidelines below:
1. Download the manifest file for the Outlook Add-in;
2. Log in to the Office 365 Admin Portal;
3. Click Settings to expand that section and then click Integrated apps;
4. In the admin center, go to the Settings > Integrated apps > Add-ins page;
5. Click Deploy Add-in;
6. Click Next;
7. Click Upload custom apps;
8. Click I have the manifest file (.xml) on this device;
9. Click Choose File, and select the manifest file;
10. Click Upload;
11. Choose the user assignments and deployment method, then click Deploy;
12. Once the deployment is finalized, click Close.
For information on how to create a meeting with VSight add-in, see here.