The ultimate solution is likely to replace what's on your internal uSD card with a good image, that restores functionality back to before the Android mod.
https://www.mobileread.com/forums/sho...d.php?t=209122
Describes the process, to make an image and install it on a larger uSD card. You would need to ask for a good AuraHD image file, over in the "Developer's Corner", and then just do the last parts of the process.
The mod should have included a means to restore the boot process, if they have messed with it so that you can't just remove the external uSD card and apply a downloaded firmware "update".
Luck;
Ken