After working number of hours I found out that 12c does not support pointing existing agent to new OMS repository…really Sad, unfortunately there is no other way other than un-install and re-install agent…
See note from oracle below:
EM 12c : How to Point Existing 12c Agent to New OMS ? => Change Location of OMS and Repository of 12c Agent [ID 1490457.1] To BottomTo Bottom
Modified:Sep 24, 2012Type:HOWTOStatus:PUBLISHEDPriority:3
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In this Document
Enterprise Manager Base Platform – Version 22.214.171.124.0 and later
Information in this document applies to any platform.
How to point existing 12c Agent to new 12c OMS ? Is it possible to change the location of the OMS/Repository of a 12c Agent ?
Reconfiguring a 12c Agent from one 12c OMS to an another 12c OMS, without a re-installation of the Agent, is currently not supported.
This is not possible to change the OMS/Repository location properties on 12c Agent’s side from one OMS/Repository to another new OMS/Repository,
like it was possible in EM 10g and EM 11g.
When a 12c Agent is re-configured to a new 12c OMS, OMS will not accept this Agent or its targets for monitoring.
In previous Enterprise Manager releases (10g and 11g), the targets discovery is initiated by the Agent.
The targets are discovered and first updated in the /sysman/emd/targets.xml file and then pushed to the OMS.
But in EM 12c, OMS is the source of truth. That means that the targets registration happens first at the OMS side and then the targets are pushed to the Agent in targets.xml file.
Hence, it is required to re-install 12c Agent from the new OMS when it is needed that an agent points to a new OMS.
There is an Enhancemenet request logged :
BUG:14532300 POINTING AGENT TO NEW 12C OMS
Note : Refer that document to help you to push/install an Agent from the EM 12c console :
Document:1360183.1 – Cloud Control Agent 12c Installation – How to install Enterprise Manager Cloud Control 12.1 Agent
BUG:14532300 – POINTING AGENT TO NEW 12C OMS
NOTE:1360183.1 – Cloud Control Agent 12c Installation – How to install Enterprise Manager Cloud Control 12.1 Agent From the EM 12c Console ?