...
curl -u admin:admin -H "X-Requested-By: ambari" -i -X PUT -d '{"ServiceInfo": {"state" : "INSTALLED"}}' http://<ambari-server-name>:8080/api/v1/clusters/<cluster-name>/services/MAPREDUCE2
Go to Ambari Web > Services > MapReduce2 > Configs > Advanced, and modify mapreduce.jobhistory.address and mapreduce.jobhistory.webapp.address to point to the new History Server host.
Restart MapReduce2 Service after saving the configurationStart Service after changing configuration from Ambari UI.