Download https://github.com/samjones246/rpgmmv-livesplit/releases/tag/v1.0.0

Drop in the OMORI mods folder, which will be located in www.

Download https://raw.githubusercontent.com/samjones246/omori-asl/master/Autosplitter.json by clicking Save As on the page.

Put it in the root directory, or where the Omori.exe executable is.

(Optional) You can change where it autosplits by opening up the Autosplitter.json in Notepad and editing it on the bottom.