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.