Ok this is very trivial question, but just cannot find answer anywhere.
I know there must be a JSON file with all the build systems somewhere, but I just cannot find
In sublime use this step
Tools -> Build System -> New Build System
Than a new build file will be opened . On saving this file , sublime will prompt the file dialogue option to save the file . Than you can see the location where sublime saves all the native build files . From this location you can edit the existing native build files .