You can try exporting it to Blender and making the fur there. Blender has amazing tools for fur - you can comb, trim, extend and puff it. Here's a model with fur I made: https://www.furaffinity.net/view/39145050/

Ok I'll try to export it to blender but the truth is that I still don't know how to make the hair since I'm a little beginner in 3d modeling ;w;

Here's a short video of how it works:
https://www.youtube.com/watch?v=Oq0q8AmTnDU
If you'll have problems with Blender, I'll be happy to help.

Thank you very much, I'm going to see the video :3

Ok, I already put the model in blender and I already understood the video you gave me, but I have a question about how can I select only part of the model, for example, I just want to put hair on the back of the head how can I do it

There are two methods. You can select model, then go into Edit mode, select faces that you want to separate (try pressing "C" for painting-like selection), and press "P" to separate them. Then you will have two different objects, and you can add fur to one of them.
Second method is more interesting. You can add a new vertex group to a mesh (in the mesh properties), then set it as a hair density in Particle Settings/Vertex groups, and switch from Object Mode to Weight Paint mode to paint the model with fur.
You can send me a note if you have problem with any of these.