There are 2 ways. File edit or manual.
File edit:
Open the npcname-e.dat from the server's system folder and find the monster that you want, and take its IP.
Then go to the bot, go at bot options -> tab-Do Not, add it and check the "Attack only NPCs in list" option.
2. Manual
Go to the area that you want and be near those monsters. At the bot programm, go to tab NPCs. There should be all the NPCs who are arround you. Find those which you are interested.
In the NPCs' info, there are the tittles also. Move the cursor over them and wait for a while so the info appear. Then, you could take their IPs. (You won't need the one with the tittle).
So take the one without the tittle and again do the same
Bot options->Do Not->Add the monster->Check "Attack only NPCs in list" and you are done.
I hope i hepled you :)