Backup Agent Takeover
Purpose: You may find that you need to adopt a device that was onboarded by a different Veeam Backup & Replication server. Maybe the old server died, or maybe you are restructuring your backup infrastructure, and want a new server taking over the backup responsibilities for the device.
If this happens, Veeam will complain that the device is managed by a different server. To circumvent this, perform the following changes in the Windows Registry based on the version of Veeam Backup & Replication you are currently using, then try to Update the Agent / Backup the agent again, and it should be successful after the registry changes are made.
Reference Material: https://forums.veeam.com/servers-workstations-f49/how-do-we-move-agent-to-associate-with-a-new-veeam-server-t79977.html