Download and install the same firmware version that's already installed. From here:
https://www.amazon.com/gp/help/custo...MQC26VQQMM8XSW
When you copy the firmware files DON'T eject Kindle from your computer, instead press and hold the power button for 15+ seconds to force a reboot. That should then trigger a firmware install.
That should restore OTA binaries so that you then can use "Update Your Kindle" again and then try to install the hotfix.
Or maybe eve better if you first check is ";log mrpi" command functional or not. If it's working then you just copy MRPI files into "extensions" folder (since factory reset removed them) and the hotfix bin you copy into "mrpackages" folder and then trigger hotfix install by using ";log mrpi" searchbar command (instead of using "Update Your Kindle" which is unavailable because you renamed the OTA binaries).
If ;log mrpi is also broken then do the first option I mentioned (firmware (re)install + hotfix install via Update Your Kindle option).