Please confirm you are running Veeam ONE 9.5 prior to installing this update. You can check this under Help | About in Veeam ONE Monitor Client, the build number should be 9.5.0.xxx. After upgrading, your version build will be 188.8.131.5254.
This update should be applied to the Veeam ONE server, as well as remote systems with the Veeam ONE Monitor Client.
Before you apply the update, make sure you have a full backup of Veeam ONE database.