How do I learn to fix the machine I run?

You can run the machine, but you cannot yet keep it running, and that gap can make you feel less than fully in control of your own work. It is not a character flaw. Operating and maintaining are two different trades that happen to share the same machine. The good news is that maintenance is learnable, and you already have the biggest advantage: you know how the machine behaves when it is healthy, because you feel it every day. That instinct is exactly what a good mechanic uses. You just need to connect it to what is happening under the panels. Ask to shadow whoever maintains your machine for even one service, and have them show you one routine task you can start doing yourself. Learn that one thing well. Then the next. Skill is just a stack of small tasks you did not have yesterday.