ASUS AX53U fixing only 36MB space how?

@frollic said before:

Create your own firmware, allocating all space, or wipe the backup firmware, and use the available space as extroot.
I want to free that backup space now, how do I do that? Creating my own firmware how? Using available space as extroot seems extremely complicated.


Where is this backup firmware staying at? mtd3 or mtd2?