If you have deleted a host target and the corresponding Management Agent target, you can retrieve both of them. To do so, follow these steps:

Discover and add the host and the Management Agent by running the following command from the agent instance home of the corresponding host:

$ emctl config agent addInternalTargets

Once the host and the Management Agent are discovered and added to the console, add each target on that host as targets to be monitored in the console, by running the following EM CLI verb:

$ emcli add_target
      -name="name"
      -type="type"
      -host="hostname"
      [-properties="pname1:pval1;pname2:pval2;..."]
      [-separator=properties="sep_string"]
      [-subseparator=properties="subsep_string"]
      [-credentials="userpropname:username;pwdpropname:password;..."]
      [-input_file="parameter_tag:file_path"]
      [-display_name="display_name"]
      [-groups="groupname1:grouptype1;groupname2:grouptype2;..."]
      [-timezone_region="gmt_offset"]
      [-monitor_mode="monitor_mode"]
      [-instances="rac_database_instance_target_name1:target_type1;..."]
      [-force]
      [-timeout="time_in_seconds"]
 
[ ] indicates that the parameter is optional

For more information, see Verb Reference in the Oracle Enterprise Manager Command Line Interface Guide.