Well, you could wait until @NiLuJe updates the one-click package with KOReader 2019.10, but I think it should be as simple as:
1. Use the one-click install package as instructed. (At this moment KOReader should fail to start properly on the Libra.)
2. Overwrite the /mnt/onboard/.adds/koreader directory (or wherever it's installed to) with
the latest release.
Edit: four minutes too late.