Correct as mentioned in the previously shared link that the solution is applicable for
Solution For CentOS 7, Debian 7, Ubuntu 14 & 16, or SLES 12 (Python 2.7)
solve this problem simply configure the Ambari Agent to use TLSv1.2
when communicating with the Ambari Server by editing each Ambari Agent’s
/etc/ambari-agent/conf/ambari-agent.ini file and adding the following
configuration property to the security section:
Regarding your query : "Is there any way to register the agent from cli once the ambari-agent is running?"
Once the ambari agent is restarted it will automatically send a registration request to Ambari Server. And you should be able to see heartbeat message in ambari UI when you click on the Hosts page in the ambari UI. The hose should be shown as green.
# ambari-agent restart