Firstly, the firmware version you are seeing is the factory firmware. Firmware version 4.12.12111 was what was available from Kobo at the time did the initial setup. And you haven't let the device update since.
The factory reset put it back to 4.9.11674 and for some reason it didn't updated when you were doing the setup. That is a bit strange as it should have done this before prompting for the user details.
As to installing the firmware, there are instruction in
https://www.mobileread.com/forums/sh...81&postcount=3. But, as far as I can tell, anywhere you could manually download the firmware either has instructions to do it or a link to instructions such as this one. And it is a frequently asked and answered question here.
You might also want to consider which firmware you use. The latest release is 4.26.16704. There have been a lot of changes since either of the firmware versions you have mentioned. Including bug fixes that you would not have seen.