Sync will update from Kuroiru to Anilist, but not other way around. For this purpose use Anilist import. You can import from any public anilist account.
Import
Wipe your kuroiru animelist
your anilist account won't be affected
Wipe
Export your kuroiru animelist
Export
note : to put this to your Anilist account first you need to import it to MAL account, then after that export from MAL to Anilist.