Change texture of a Lego Microgame Minifig

Hello

I’ve been working with Unity for a short time and I’ve already gone through a few tutorials.
In general, I also understand prefabs.
I’ve been trying to understand how the prefabs work for the minifigures in the Lego Microgame for several hours.
more precisely, where the assignment for the appearance takes place. So where is the PNG file d644726.png (Front T-Shirt) assigned to the Adventurer(Prefab of the Minifig), for example?
I want to create a custom Minifig just bei use a Prefab and only use my own Textures.

I would be happy if someone had tips for me!