This is what I found after cross-checking various threads and sources:
The best source out of the ones I found is this paper from the university of Tulsa about sculpting leather.
Essentially, the process boils down to the following:
A. We need to soften our piece of leather in order to be able to shape it. In order to do that, we dip the leather into water. The water needs to be hot, but to the point where we can dip our hand into. Also, it needs to be wet in every part of it, but not to the point where it’s dripping water when you take it out.
B. We take it out of the water and put it on the mold. Then we shape and sculpt it it by pressing either with our hands or y using a tool (i.e. the back of a spoon.)
C. No that the piece of leather is shaped to our liking, we need to harden it in order to stay in that shape. To do that we can either bake it in an oven (not with the mold though, because the leather will stick on the metal) or by dipping it into boiling water. The method with the boiling water is the fastest (taking from 20 to 120 seconds) but if our piece of leather is large, then we will need to find a large enough container to boil the water in.
D. After harden it through heating it, the last step is to apply wax on the leather. It’s better to apply the leather from the flesh side, otherwise the wax needs to go through the leather to be absorbed. We keep waxing the leather until it cools down to a point where it doesn’t absorb the wax anymore. The wax will harden even more the leather.
Thank you both for taking the time to reply to my question. If there is anything you'd like to add, please do so.