How do I get a separate animation to work with FBX model?

Questions
1

I have a model from mixamo and have downloaded an animation without skin to try and combine them in three.js.

  1. if the animation was downloaded while the same model was selected, it works in three.js.
  2. if the animation was downloaded while using a different model, it does what the image above is showing (floating model)
    We need it to work for scenario 2 but don’t know why it doesn’t work.

Any help will be greatly appreciated.

Thanks!