The instruction and files you need are in
https://www.mobileread.com/forums/sh...d.php?t=212162. But, the first post hasn't been updated for a while. You need to look towards the end for discussion of 4.1.x or 4.2.x firmware.
There is also a method using a change to the config file. See
https://www.mobileread.com/forums/sh...56#post3531156 for details.