That should work on its own. Mixing values are pulled from SkeletonDataAsset's Animation State Data -> Mix array
public String[] fromAnimation;
public String[] toAnimation;
public float[] duration;
it is easy to edit in the inspector for the SkeletonDataAsset, however you can also add new mixes at runtime as well using AnimationStateData.SetMix(from, to, duration)
The idea is that From
To over Duration means if you are currently playing "Walk" and you do SetAnimation(1, "Run") then it will take Duration seconds to blend from Walk to Run. Similarly if you want to blend from Run to Walk you will need to create another entry that is Run
But anyway, click the Add Mix button ๐