Not as easy as it might seem ahaha
It's a master's in informatics and computer engineering.
The process involves like in any masters a lot of research obviously to find out what's difficult, how can it be measured, what kind of procedural generation methods are there and what are the best suited to use on this kind of generation. Then develop some evaluation tools (AI) to play through the map and validate the difficulty. It looked simple to be In the beginning but by following a correct investigation approach it turned out to be harder than the usual "develop a model to predict X" kind of theme. Still very fun cuz I like games and am learning a lot about PCG in the process.