This has nothing to do with crackmes. This field is called exploit development. Though you need reverse engineering knowledge, exploit dev steps it up way more because you have to find bugs by reading assembly.
That being said, exploit dev is a mindset, but you can learn the basic-beginner methology by following LiveOverflow’s videos on YouTube.
By the way, for this certain type of pwnable there’s a write up of mine explaining the internals of format string attacks.