First, decompile, modify, and then select a folder to compile back. After compiling, you need to sign the apk package.
It should be noted that the modified apk cannot be stored with the installed original APK, nor can it be overwritten. Before installing the modified apk, only the originally installed program can be deleted.
Similar softwares include apktool, apk+deb, etc.
Requires a Java runtime environment. Need to have a certain foundation of java language.