Oh, that's pretty easy.
In Unity go to the "Animator" tab.
It should show the FX your model is already using. (If it doesn't. Find its FX layer, click on it. THEN open the Animator tab)
Go down and look for anything that says 'Face' or 'Expressions'.
Go to the ones you want to change. Click on them.
On the right hand side a menu will open. At the VERY top of it is the name of the animation its using.
You can remove it and change it with the animation you want either by searching for it or dragging and dropping it in from the asset folder. (Inside the asset folder it will have a bunch of other folders inside and one of them should contain the animations for face expressions)
