IIRC PW1 with that firmware can be downgraded to 5.4.x by copying older firmware update bin and forcing device reboot by holding power button for 20? seconds
while it is still connected via USB cable to your computer. (if you disconnect it the bin file would be deleted.)
And then after successful firmware downgrade you would use jailbreak method for that older firmware.
https://www.mobileread.com/forums/sh...d.php?t=186645
For info on how to get a link to download that older firmware you should read my comment here:
https://www.mobileread.com/forums/sh...20#post4291520
And also check what firmware build numbers where available for you Kindle model here:
https://www.amazon.com/gp/help/custo...deId=200203720