You must find the fortess at the command set and there you add them.for more details i cannot help yyou.
Or, if you don't want to go through all of that, you can just delete any heroes you don't want in the Men faction, so if you didn't want Eowyn and Eomer, just delete their two names from the playertemplate.ini, or you can add them to a different faction in case you want them back later and don't remember how exactly to get them. As said above, the other way is to edit the comandset.ini of the Men faction fortress, which can be a bit confusing, so I usually just delete the heroes names that i don't want or don't use. Hope this helps!
I haven't been active here in a long, long time.. Maybe this game will steal back my attention. Until that happens, I guess I'll just play Call of Duty 4!