Since all of that is still work in progress you would need to read through all the comments on that GitHub issues and apply manually all the edits and files replacements.
Like, read those 2 comments:
https://github.com/koreader/koreader...ent-2089432884
https://github.com/koreader/koreader...ent-2089646786
Or monitor that discussion in order to see when the "pull request" gets merged and after that wait for next nightly build of KOReader and install that build.