Just open blender and put the prefer models into your scene by clicking File -Append - and then go to your downloaded folder.

For better organization the models are put in different named collections. Collection Midpoly has the more detailed models in it and the collection Lowpoly has the low crow models.

Change the gloss of the roughness map

Your scene is always in different light conditions, so therefore the plumage needs different strength of roughness map in order to better show off.
You can change that in the material shader by changing the color ramp.

Flexible Mandible

To achieve more realism and flexibility, the mandible was modeled independently of the photoscanned crow.
You can add the mandible in the same way as the crow model. You can easily move the mandible by just select the mandible mover (Empty)