From the menu screen of the KokuDoku app, log in to Notion.

Log in to Notion on app
Tap Next, then Allow Access.

Check what accessed by KokuDoku

Allow access to Notion from KokuDoku
Return to the KokuDoku app and tap “Use this database.”

Choose the database to export to
Once everything is set up, tap Export ****All. Your highlights will then be viewable in Notion organized by book. (The first export may take some time, so please be patient.)

Tap “Export All” and sync it