Unregister vCenter with External PSC or Embedded PSC - Remove vCenter from ELM

Prerequisite:

1. Make sure you have root and administrator@vsphere.local credential

2. Take offline snapshot of vCenter servers in ELM.

vCenter Server Appliance:

1. Power off the vCenter Server Appliance you are decommissioning.
2. SSH to one of the other working External PSC or Embedded PSC/vCenter appliance within the same SSO domain via root
3. To enable the Bash shell, run:

shell.set --enabled true

4. Run the shell command to start the Bash shell and log in.
5. Run the cmsso-util unregister command to unregister the vCenter Server Appliance:

   cmsso-util unregister --node-pnid vCenterServer_System_Name --username administrator@your_domain_name --passwd 'vCenter_Single_Sign_On_password'

   Where vCenter_Server_Appliance_System_Name is the FQDN or IP address of the vCenter Server Appliance that you want to decommission. Please enter the vCenter_Single_Sign_On_password in quotes.
   
   Note: there is downtime involved in executing the cmsso-util unregister command. It will restart the services on the node where you are executing the command.

6. Delete the vCenter Server Appliance that you no longer need from the vSphere inventory.

Form more details: https://kb.vmware.com/s/article/2106736