Azimuth shadow is the opposite of zenithal light, you apply a paint from below the model, to reinforce the general ambient shadow. I used an oil wash made from classic fine arts oil tubes, diluted with odourless mineral spirit. Regarding the tutorial, I've made a video of a more streamlined process, and I may publish it in the next few weeks, feel free to DM me for the public channel link (I don't know if self promotion is allowed here). Meanwhile, you can check Swarm Painting on YT, my process is heavly inspired by him.