Doubts to edit animations of an asset from asset store.

Hi, I'm pretty new about deal with animations in Unity. Im trying to make small changes in the aninations of this package:

https://assetstore.unity.com/packages/3d/characters/humanoids/sci-fi-soldier-29559

But for some reason, when I select any animation and try to apply the humanoid animation type, the asset loses the animation clip. Besides that, I'm struggle to find a way to edit the animations, already tried to look some tutorials at youtube, but none of them worked for what I want. need this for a college project, please help.