In the Symantec Management Console: Settings>Notification Server> Site Server Settings.

On the left hand side, drill down under Site Servers to the Site server you wish to be host.
Expand the menu under this server, click Manually Assigned Agents.
Click New.
There are many pre-built “targets”, but you can also create a target based on specific criteria.
For example:
To Build a target for a specific computer:
Click Built target, then click Add rule. 
NOTE: it states ‘Start with all resources:.  Otherwise the first drop down can be misleading.
To select just one computer, select: ‘exclude resources not in’.  In the second drop-down select ‘Resource List’.  In the last field you can type the name of the computer you want assigned.
At this point, if you click OK, this list will be saved with a default name.  You want to click Save as at the top of the page, and type a name for this list.
Then you will need to select that name in the target list, and move it over to be a selected target.