How to make skeleton horses with skeletons on them spawn in soul sand valleys?

i went to misode and then its biome generator and selected the preset soul sand valley but theres so many things in misode i dont know how to add a skeleton horse spawn
and when its done i dont know where to put it in my datapack, i assume in the minecraft folder just like how i overwritten a recipe but i dont know what to call the folder in the minecraft folder