After the vRealize Orchestrator Server is rebooted, again open the URL https://<IP or FQDN of the Orchestrator Server>:8281/vco/ and Download Orchestrator Client Application.
After the download is complete, extract it.
Open the vROWorkflowDesigner.exe and enter the IP of the vRO and the SSO password.
It will open up the vRealize Orchestrator Server.
Click On Workflows -> vCenter -> Configuration -> Add a vCenter Server Instance.
Click on the Green Play button on the top to start the workflow.
Mention the necessary details about the vCenter Server and click Next.
Mention the vCenter Credentials and click Submit.
A workflow will be created.
You can verify the vCenter in the Configuration Tab.
Start the workflow of Register vCenter Orchestrator as a vCenter Server extention.
A workflow will be created and vRO will be registered in vCenter Server.