Send message to a specific client from server

[Sandbird]

In order to send global messages from server - > client we use this:

_message = format["Hello world."];
[nil,nil,"per",rTITLETEXT,_message,"PLAIN DOWN"] call RE;
sleep(5);

If i want to send the message to a specific user only that i get from :

 

_player  = _unit getVariable["bodyName", "nil"];

 

how will i 'rephrase' the above command ?

 

-Thanks