the models won't export.

I apologize for posting in this thread, but I wanted to quickly send a message while I still have an internet connection, rather than searching for the right topic. Besides, this question is also touched upon here. I would like to understand what is meant by "recoloring" units. I've noticed that some mods have excellently recolored creatures, and I'm trying to do the same, but I'm not succeeding. I change the model and textures of a Death Knight to those of a Paladin, and the result is some kind of mess with a smeared helmet and no eyes riding on a horse. I don't need a Paladin to be there; I want the Death Knight to have armor of the same color. Also, I can only replace the textures of a specific part of the monster, for example, the entire body at once, but I can't recolor just the sword separately. What am I doing wrong? Do I need to create the textures myself and then link them? Or should I use existing ones? For example, if I recolor a dragon, the shine in its eyes always disappears. I hope for an answer.