You'll need to update vRO vCenter plug-in. You can pick an updated plug-in binary file from this page - https://communities.vmware.com/docs/DOC-32872
Once you download the new plug-in file, unzip it, and update the existing plug-in using vRO Control Center > Manage Plug-ins.
thank you llian. after updated vRO vCenter plugin, i was able to add vCenter 6.7. thank you again