After registering HSM with PHM, you need to associate appropriate hosts available in the vCenter Server with the HSM.
This enables PHM on each host. HSM informs PHM on any change in the managed host list. PHM associates the managed hosts available in a vSAN cluster. When a host is associated or dissociated with PHM, vCenter Server event gets generated. For detailed information about associating and dissociating hosts, refer to the respective OEM-provided documentation.