How can you fix the mod MORE PLAYER MODELS?

I downloaded myself in minecraft MORE PLAYER MODELS but if I want to get used to an animal or anything else in the mod then it will not work. My skin stays the same.

In which version do you play?

1.12.2

Then good question, do you use Optifine or Forge at the same time? If not, I would give it a try

Unfortunately still does not work.