The password of the Oracle VM Agent cannot be modified in the Authentication tab of the Oracle PCA Dashboard, nor with the update password command of the Oracle PCA CLI. If you need to change the agent password, use Oracle VM Manager.
When you upgrade to Oracle Private Cloud Appliance Release 2.3.x then the management nodes are re-installed with Oracle VM Manager Release 3.4.x. Its API is different from the one in Release 3.2.x. As a result, you cannot modify the Oracle VM Agent password on compute nodes unless they have also been upgraded to the matching Oracle VM Server Release 3.4.x.
If you must reset the Oracle VM Agent password, do it either before upgrading to Oracle PCA Controller Software Release 2.3.x, or after all the compute nodes have been upgraded to Oracle VM Server Release 3.4.x.
Instructions to change the Oracle VM Agent password can be found at the following locations, depending on your current version of Oracle VM Manager:
If you are using Oracle VM Manager 3.2.x, see the section entitled Changing Oracle VM Agent Passwords on Oracle VM Servers in the Oracle VM User's Guide for Release 3.2.
If you are using Oracle VM Manager 3.4.x, see the section entitled Change Oracle VM Agent Passwords on Oracle VM Servers in the Oracle VM Manager User's Guide for Release 3.4.