You can manually mark chapters as [Read] or [Unread] by following these steps.

1. Open the chapter list screen of the title you want to mark.
2. Tap the [mark] button to switch to "Mark" mode.
3. Tap any chapter to change its mark between [Read] and [Unread]. You can also use the [smart select] button to mark multiple chapters by criteria.
4. Tap the "Done" button to end "Mark" mode.