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 188.8.131.5201 or 184.108.40.20654. After upgrading, your version build will be 220.127.116.1101.
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.