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Once you have installed OC on a device for one Office product (e.g. Word), the OC will automatically be available for the two remaining Office products (e.g. Excel and PowerPoint). 

Updating the manifest file

When updating the manifest.xml file (NOTE: this does not apply to the case where the website itself has been updated) make sure to increment to ID-field of the manifest file. 

If a user doesn't see the effects of the changes, try following the steps under "Remove an add-in from local cache" at: https://docs.microsoft.com/en-us/office365/enterprise/use-the-centralized-deployment-powershell-cmdlets-to-manage-add-ins?redirectSourcePath=%252farticle%252f94f4e86d-b8e5-42dd-b558-e6092f830ec9#delete-an-add-in