Hi, if you want to contribute to this project this document may help you. If there are any questions just create an issue.
I usually get the currently installed apk by copying it from /data/app/[package name]/base.apk.
The Fastlane tool might help you here. If you have it installed then check out the available commands.
There are a bunch of tools out there for decompiling and digging through apks. The one I've found easiest to use is jadx in which you can open apks directly.
If you want to help the development you just can make a pull request containing a new hooks.json in a folder with a matching version code. You can find the version code folders in here.
If you need help with finding the hooks (methods / fields) you should take a look at an older hooks.json and there you'll find, for every method/field, a brief explanation where it should be located and how to find the right one.