It is not too hard and you can definitely do it! It’s like a puzzle - you will get stuck at times, but if you keep going then you’ll get there.
APK files are just zip files, so you can unzip it to see its contents. From there, a java de-compiler get you a version of the source code. It will have random variable names and no comments, so it will take some digging to find and reverse the api layer.
Or, who knows, you could get lucky and find an openapi spec file and auth.txt. Worse apps have been developed.